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1. T will try said Pat If the operating system has a GUI then the user will use the mouse pointer to double click on a program or select it from a pull down menu The machine language instructions in the operating system will then ask the secondary storage device that holds the program to send it one number at a time to the I O location that the storage devices is attached to The CPU will then take each of these numbers and place them into an unused section of RAM After the CPU as finished copying the program into RAM the operating system will then tell the CPU to start running the machine language instructions of this program Pat then took a marker and added another vertical line above the line that represented the operating system This second vertical line represented the application program after it was loaded into RAM Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 72 77 Memory Map Inside Outside computer Computer ROM X lt q Keyboard Leiner I CPU or Z lt gt Hard Drive XXX H KA XXX 1 XXX RAM Application Program Operating System loaded into memory That is correct Pat I said you seem to be learning this information rather well One thing I have not mentioned until now is that a PC usually has an extra piece of hardware in it called a Direct Memory Access controller or DMA controller for short This controller is able to directly copy numbers
2. I consider myself to be an aspiring universal technologist which means that I am interested in all aspects and areas of technology and I strive each day to learn something new about technology that I did not know before I assume you are reading this book because you too are interested in technology and specifically there is something about computers that you find attractive You and I have something in common then because I fell in love with computers when I was a Senior in High School in 1982 and I have become ever more deeply involved with them since that time The early 1980s was a wonderful time to become involved with computers because inexpensive PCs Personal Computers became available for the first time These machines generated a great deal of excitement and this excitement resulted in a wide range of what I call first generation educational materials being written for these machines What I mean by first generation educational materials are the educational materials that are created for a technology just after it becomes available When a technology first appears the people who write about that technology assume that almost nobody knows anything about it and therefore authors are especially careful to move slowly and not miss critical information Beyond this many of these authors were beginners with the new technology themselves not too long before creating their educational materials and so all the critical little piec
3. O NO R oO CPU a Registers 10 a o co Run One Instruction O M O RO O N o Instruction Table 169 Loads the number in the memory location immediately following the instruction s memory location into register A We have just successfully run or executed our first instruction I said and now the number 10 is in register A waiting to be added to the number 5 The last thing we need to do is to update the Program Counter register to point to the address of the memory location that will hold the next instruction I then erased the old value that was in the Program Counter and replaced it with the number 2 I also made the program counter point to memory location 2 Pat said It seems that the next instruction we need is one that tells the CPU to add 2 numbers together I smiled and said I agree lets come up with another number between 0 and 255 say 105 and this will represent an addition instruction I then wrote the number 105 in the next row of the Instruction Table and also Copyright 2007 by Ted Kosan 910 911 912 913 914 915 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 Version 1 21 Computer Systems 32 77 wrote it in memory location 2 in the memory map How do you think this addition operation should work Well said Pat we can have
4. 1035 I smiled and said We have successfully completed a small program what 1036 do you think 1037 Pat said I am still fuzzy about a number of things but I am really enjoying 1038 this so far 1039 I am glad you are enjoying this information Pat There are thousands of 1040 careers in the world that have this information at their core and if you 1041 continue to study computers perhaps you will work with them some day Copyright 2007 by Ted Kosan 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 Version 1 21 Computer Systems 39 77 What are some of the things you are fuzzy about Machine Language Pat pointed at the Commodore 64 s screen and asked If a CPU is programmed with opcodes how can it also be programmed in BASIC To answer that question perhaps it would be best if we went back to the early days of computers When the first modern computers were created in the late 1940s and early 1950s the only way they could be programmed was using opcodes The programmers back then would create a program by drawing a memory map like we did on the whiteboard and then write CPU opcodes and needed data into the memory locations They would then enter the series of numbers they had written into the physical computer s memory using swi
5. After this first machine language instruction has been executed the Program Counter is set to the next machine language instruction in the sequence it is then executed and so on This next part was important so I dropped the level of my voice a little and said if there is ever an instant in time when the CPU is ready to execute a machine language instruction and the number it pulls from the memory location that the Program Counter is pointing to is not part of the program that is running the computer will also lock up Most of the time that a computer locks up this is the cause You mean something as simple as that can lock up a computer Pat said Why is that Copyright 2007 by Ted Kosan 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 Version 1 21 Computer Systems 46 77 A CPU Is A Very Dumb Device Do you remember when I said earlier that a CPU was one of the dumbest things in the world I asked Yes said Pat it was when we were talking about the CPU being like a simple calculator The reason that a CPU is so stupid I continued is that it needs to be told exactly what to do step by step the whole time it is running In order to get a feel for how stupid this is imagine that you had to be told exactly what
6. but we are learning more about it all the time Lets go back to the combination lock and see if we can describe a lock that has some physical parts and some cyberspace parts This lock will still have a shackle so that it can lock a locker and it will still have a 3 number combination Instead of having a dial though it will have a keypad so that a human can enter the combination Instead of metal parts controlling whether the shackle is able to be opened or not it will have a solenoid A solenoid Pat said What is a solenoid Have you ever turned a nail into a magnet by wrapping a bunch of wire around it then putting electricity through the wire I asked Yes said Pat I read how to do that in a science book and when I turned it on I was able to pick up paper clips with it I continued A magnet made using this technique is called an electromagnet A solenoid uses an electromagnet to pull on a metal arm in one direction and a spring is usually used to pull the metal arm in the opposite direction when the electricity is turned off The result of this is that when the electricity is turned on the arm moves up against a stop in one direction and when the electricity is removed the spring moves it against a stop in the opposite direction In our lock the end of a solenoid s arm can be used to either allow the shackle to lift or to prevent it from lifting Solenoids are on off devices and computers love
7. and what makes the I O locations special Pat replied The I O memory locations are special because they can can have numbers copied into them and out of them by both the CPU and bya device that is outside the computer That is why the I O locations have a hole in them that face the CPU on one side and a hole that face the outside world on the other side Very good Pat I said Now the CPU talks to the storage device and asks if it contains numbers that represent an operating system If the storage device replies that it does the CPU requests that the device send the operating system s numbers into the I O location one number at a time and the CPU in our model copies each of these numbers into RAM Most of these numbers represent machine language instructions As I said this I pointed to the vertical bar at the bottom of the RAM section of the memory map which represented the operating system s numbers Copyright 2007 by Ted Kosan 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 Version 1 21 Computer Systems 69 77 After the core of the operating system has been copied into RAM I said the last instructions in the ROM sets the CPU s Program Counter to the beginning of the operating system s machine language instructions in RAM and then the ope
8. but someday I will help you to learn to program in BASIC if you would like We will however be discussing more about what a computer program is in a little while What Do The Numbers In Memory Locations Mean Pat looked at all the numbers on the screen that were obtained from the Commodore 64 s memory map and then asked What do all of these numbers mean That I told Pat is one of the great secrets behind the power of a computer Remember when I told you that a computer s memory locations can contain anything a human mind can think of I remember replied Pat Well the way it does this I said is by having the number that is in any given memory location represent an idea that is in a human s mind For example lets say that we write a program that works with apples In our program we are going to have the number 1 represent red apples and the number 2 represent green apples We will use memory location 5 to hold the type of apple we are currently working with If I place a 1 into memory location 5 what kind of an apple is it now holding Pat thought for a moment and then said A red apple Correct I said and if we placed a number 2 into memory location 5 that memory location would then contain a green apple Of course we can not place a physical red apple into memory location 5 but by having a number Copyright 2007 by Ted Kosan 641 642 643 644 645 646 647 648 649
9. 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 Version 1 21 Computer Systems 53 77 in a PC is usually much smaller than the amount of RAM it has After the CPU has finished executing the POST code in the BIOS ROM it needs more machine language instructions to run The BIOS ROM however being relatively small has very little room for extra instructions The CPU s Program Counter could be reset back to the beginning of the ROM and the POST code could be re executed but this would result in the CPU re executing the POST code over and over again and the computer could not be used to do any useful work After the POST code there is only room for a small number of final instructions for the CPU and if it cannot find any more instructions its Program Counter will run off the end of the ROM memory into garbage memory and the numbers in the garbage memory will guickly lock the CPU up Therefore the remaining instructions in the ROM should be used to tell the CPU where to find more instructions but where is it going to get them from Pat Pat studied the memory map for a while then said The CPU can t get more machine language instructions from RAM because the computer was just turned on and all the RAM locations contain garbage numbers It also can t get more machine language instructions from the ROM because the ROM is fairly small and it has already used most of the instructions in there Hmmm com
10. 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 Version 1 21 Computer Systems 23 77 in this case the number 1 represent a red apple we can place a reference to the idea of a red apple into that memory location Any idea you can think of no matter what it is we can associate a number with that idea and thereby enable a computer to work with it Go ahead come up with an idea Pat Pat thought for a little bit then said Boat I said We can associate the number 47 with the idea of a boat Come up with another idea Pat said Cat 234 I said See no matter what idea you think of I can think of a number to represent it Contextual Meaning After this explanation Pat s eyes light up and one could almost see wheels and gears turning behind them That s amazing cried Pat I never would have guessed that a computer works like this After thinking a bit more though Pat asked But if a memory location can only hold a number between 0 and 255 how can it possibly be capable of representing all of the millions of ideas that a human can have That is a wonderful question Pat I said and the answer is a concept called contextual meaning Contextual what Asked Pat Contextual meaning I said I will give you an example that will help explain what it is I stood up walked out of the room waited a fe
11. brick wall that is 50 meters long 5 meters high and 1 2 meter thick The first thing that needs to be done is to hire a backhoe crew to dig a trench 50 meters long and make it deep enough to put the bottom of the wall below the frost line This digging might take 2 days Next a cement form making crew needs to be hired and it might take them another 2 days to put together the forms in the bottom of the trench for something called a footer which is what the bricks will sit on A cement crew is then contracted to fill the form with cement and it might take a week for the cement to cure to the point where bricks can be placed on it Finally brick layers are hired to slowly and carefully assemble the wall brick by brick This might take another two weeks During all this time captain Kirk in his slower time frame has moved perhaps an inch or two Now imagine that captain Kirk looks up and he sees what A brick wall suddenly appeared out of nowhere cried Pat The wall was not built using magic but to captain Kirk in his slower time frame it looks like it was Yes I said to captain Kirk it looks like a brick wall suddenly appeared in front of him as if by magic This time frame difference is the part that is missing from our models of a computer A computer is only capable of doing very simple operations like copying numbers from memory into the CPU copying numbers from the CPU into memory and simple mathematical operations
12. playing computer and video games During my first semester 280 attending college I nearly flunked out because I spent most of my time 281 playing computer games instead of attending class and doing my 282 assignments A significant number of my students over the years have 283 fallen into the same trap and I have noticed that the problem is getting 284 progressively worse 285 If you want to succeed as a computer technologist then you absolutely 286 have to sacrifice the activities in your life that waste your time and 287 sguander your energies 288 Figure out what math is all about 289 If you are already proficient in math then you can skip this section If 290 you are one of the people who struggles with math however you are 291 going to need to do something about this The solution is not very easy 292 but at least it is straight forward What you need to do is to start from 293 square one locate a good arithmetic book and work through it cover to 294 cover This means starting at page one reading each chapter until you 295 understand the material and then work ALL of the problems at the end of 296 the chapter 297 When you have finished the arithmetic book locate a good algebra book 298 and work your way through that one too Keep working through 299 increasingly more advanced mathematics books indefinitely Visit used 300 book stores on a regular basis and start accumulating math books of all 301 types The Internet is the
13. ETAN EEE 39 Assembly Langua gerisi ack ee css vas aaa as ans EEEE AAEE RLU a 39 The 6502 CPU s Instruction Set sesesesssseseseseserseseserseseseseseseesesesososseseo 40 Low Level Languages And High Level Languages 42 Compilers And Interpreters ccccscsccscoececescscsecscceesesccesceeceeseeesescseseseneees 42 The Three Types Of Computer Memory een 43 RAM Random Access MEMOTY ccccsccsccsccecssccecesccsceeceseescesceesseceeeeeeeoeenes 44 A CPU Is A Very Dumb DEVICE 3 04 r oe tna kenasededs 46 ROM Read Only M FM inate salon v 47 ESD Electro Static DISChargEe z sstll ycckc rovno did dano do v an 49 BIOS AME POS Tai E k dy 52 VOM OV O ARROS o o oo 53 Loading An Operating SYSLEMsissttvlnd rivno sovu slak cos kri vala t rosou 57 Operating Systems Bridges To Cyberspace 59 Systems WIS V SES O v 60 Physical Parts Are Costly And Constraine d cccccececseceenececeeeeeeeeeneenes 62 Moving Parts Into CYberspa co ss5isska sd V A Rate 63 A Lock Made Of Physical Parts and Cyberspace Parts ccceceeeeeeeeeees 64 Microcontrollers Computers On A CHip ccccccececcscececeeceeseneeecseeenenene 65 Operating System The Part Of A Computer Which Is Made From Cyberspace Par lS sui sd stado sussex E A la dt A 66 Application PrograniSzik et ud diakadonidoseda see dena a a RA S 67 Computers Without Operating SystemS ssesesessesesesessssoseses
14. Pat Do you also remember what context and contextual meaning are I asked Yes said Pat context means the circumstances within which an event happens or the environment within which something is placed Contextual meaning is the meaning that the context gives to the events that happen or things that are placed within it Very good Pat Now it is time to give you my explanation for what Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 60 77 cyberspace is I said Cyberspace consists of all of the ideas that are currently bound to numbers in any computer anywhere in the physical universe through contextual meaning Pat sat quietly for a while with eyes staring off into space thinking about what I just said Finally Pat blinked looked at me and said When you described what cyberspace was a picture came into my mind and in it were millions of computer memory locations laid out across the Earth with millions of ideas floating above them and they were connected to each other by threads of contextual meaning Some people I said think that there really is a world of ideas that is separate from the physical world and perhaps some day we will know what ideas actually are Even if we do not know exactly what ideas are yet though we do know that it is the computer s ability to easily move ideas into and out of cyberspace and easily manipulate ideas when they are there that giv
15. RAM and ROM this third kind of memory which is called Input Output or I O memory also consists of memory locations that can hold a number between 0 and 255 As I was saying this I drew evenly spaced horizontal lines in the I O memory part of the memory map to represent its memory locations I then erased a little opening on the left side of each of these I O memory locations Notice that I have put an opening in the left side of each of these memory locations to show that the CPU has access to each one of them just like it does with the RAM and ROM locations Instead of starting with a hard drive though lets see how something simpler like a keyboard is attached to a computer The first thing we need to do is to show on our model what is inside of the computer and what is outside of it By inside and outside I do not mean inside and outside the box that the PC is in I mean what is included in the core part of the computer system and what is outside of this core I then drew a vertical dashed line to the right of the memory map and said Everything to the left of this vertical dashed line can be considered to be inside the core of the computer and everything to the right of it is outside I then drew a small horizontal rectangle to the right of the dashed line and wrote the word Keyboard inside of it Finally I pointed at this rectangular model of a keyboard and said when you press a key on a keyboard Pat
16. and 255 I said as I started writing numbers between 0 and 255 in the boxes and while the computer is running there is never a time that a box does not have a number in it Another name for a number between 0 and 255 is a byte see Fig 3 If a number larger than 255 needs to be worked with it is spread across two or more boxes These boxes are called memory locations and this vertical rectangle is called a memory map because it shows where the memory locations in a computer are located in relation to each other Some computers have a small amount of memory locations and some computers have an enormous amount Copyright 2007 by Ted Kosan 468 469 470 471 472 473 474 475 476 477 478 479 489 490 491 492 493 494 495 496 Version 1 21 Computer Systems 18 77 Pat studied the memory map I had drawn then said How many memory locations are there in this computer while pointing to the computer under my desk How many do you think there are I asked Hmmm said Pat while thinking for a few moments A hundred More A thousand More A million I smiled and said More A billion Yes I said This computer has around a billion nena memory locations each holding 1 byte and some computers have significantly more than this The metric prefix for a billion is giga and so this computer has a gigabyte of storage in is memory
17. and if it does not perhaps one half to one hour of time is required to do so We will not even bring up the fun involved with locating and making sure all of the needed device drivers are installed correctly We will make this easy and assume that the operating system is already installed More likely than not the computer is using the Windows operating system so lets power up and wait for it to boot and wait and wait for over a minute in most cases The GUI Graphical User Interface that finally comes up is nice but the level of complexity that the user is presented with is astounding when compared to the simple user interface that a machine like the Commodore 64 presents Up to this point things are bad enough but unfortunately they are about to become worse Search as much as you like but you will not find the software tools needed to write even a simple program on the machine The early 1980s computers presented a programming language as the first tool that a user encountered after booting the machine With most current Copyright 2007 by Ted Kosan 113 114 115 116 117 118 120 121 122 123 124 125 126 127 129 130 131 Version 1 21 Computer Systems TET computers however a programming language is not even included with the computer What this means in my opinion is that a beginner who wants to learn about the fundamentals of computers today will find this task significantly mo
18. called operation codes or opcodes I then wrote the word Opcode at the top of the column that contained the instruction numbers and above the descriptions column I wrote Operation Description see Fig 10 Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 33 77 Memory Map Figure 10 ei ake ed A N wo A GI CPU Registers 10 x o co Run One Instruction O ON O RG N Instruction Table Opcode Operation Description Loads the number in the memory location immediately following the instruction s 163 memory location into register A Adds the number that is in register A with the number in the memory location immediately R following the instruction s memory location The answer is placed into register A 938 After this was done I said Press the run button and we will walk through 939 executing the next instruction 940 Pat pressed the imaginary run button on the whiteboard and I proceeded 941 The CPU looks at the Program Counter and sees that the next instruction 942 that it should execute is in memory location 2 so it copies the number that is 943 in that memory location which is 105 into the Instruction Register I then 944 erased the 169 that was in the Instruction Register and replaced it with 945 105 The CPU then looks at the 105 that is in the Instruction Register 946 matches it with 105 that is
19. electronic circuits in the chip were being damaged by ESD The chip manufacturer sent some of their engineers to the Tire Tele plant to observe how the units were being assembled and they discovered that none of the people on the assembly line were using anti static protection devices or procedures One anti static procedure that all people who work with computer chips use is to make skin to skin contact with a person before handing a computer chip to them The skin to skin contact allows the static electricity level between the two people to equalize which will prevent an ESD spark from traveling into the computer chip when it is handed over As soon as anti static equipment and procedures were put into place in the Tire Tele facility their ESD problems disappeared Who would have thought that such a small thing as little sparks could cause such a problem said Pat What is your second story The second story happened when I was visiting a High School I replied in order to demonstrate a computer interface board I had built I was placed in a large carpeted room along with other people who were demonstrating things to the students and the carpet caused a great deal of static electricity to accumulate in the room The computer interface board I had made contained a speech synthesis chip on it that would take numbers as input and turn these numbers into various words T had written a program that made the chip re
20. if you are wrong you have to sort all of the resistors in this drawer I then pulled a plastic drawer from one of my storage cases which was filled with a bunch of miscellaneous resistors and placed it on the table Pat studied the tangle of resistors in the drawer for a few moments then said I don t know what resistors are but I will sort them if I lose You will have to show me how though But there is no way I can lose this one I smiled and said Bring up a browser on my computer locate a search engine and type the following Copyright 2007 by Ted Kosan 399 400 401 430 Version 1 21 Computer Systems 16 77 Von Neumann Martians Pat proceeded to do this and included in the search results was a link to a web page that contained the following passage The Curve of Binding Energy by John McPhee 1973 Farrar Straus and Giroux pp 104 105 Not all the Los Alamos theories could be tested Long popular within the Theoretical Division was for example a theory that the people of Hungary are Martians The reasoning went like this The Martians left their own planet several aeons ago and came to Earth they landed in what is now Hungary the tribes of Europe were so primitive and barbarian it was necessary for the Martians to conceal their evolutionary difference or be hacked to pieces Through the years the concealment had on the whole been successful but the Martians had three characteristics too strong to
21. in the computer s memory locations Sure I said the command that BASIC uses to peek into a memory location is PEEK lt address gt and we can use it together with the PRINT statement to print the contents of any memory location to the screen I had BASIC show us the contents of memory locations 0 1 and 2 which contained the numbers 47 55 and 0 respectively Notice that these three Copyright 2007 by Ted Kosan 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 Version 1 21 Computer Systems 22 77 numbers are between 0 and 255 We could continue typing in PRINT PEEK statements to check the contents of higher memory locations but BASIC can also do this automatically if we write a program that tells it to do this I then typed in a short program and had BASIC run it What I just typed on the screen is called a BASIC program I told Pat A program consists of instructions that tells a computer exactly what to do step by step and this specific program tells the computer to peek into memory locations 0 through 200 and print the number that it finds in each location to the screen Again notice that there is no memory location that has a number that is less than 0 in it and none that have a number greater than 255 At this point I am not going to explain how BASIC works I said
22. loosey means that a nut or bolt should be turned to the right or clockwise to tighten it and to the left or counter clockwise to loosen it For our CPU instructions we might use LDA to represent the load register A instruction ADC to represent the add to register A instruction and STA to represent the store register A instruction As I said each mnemonic I wrote it to the left of its opcode in the Instruction Table and when I was done I wrote the word Mnemonic at the top of the new column Now we need to figure out how the STA instruction is going to work We know that the number we want to copy to memory is already in register A but how is the instruction going to know which memory location to copy this number into Pat thought about this problem for a while then said Since the LDA and ADC instructions both needed to use the numbers that were just after them Copyright 2007 by Ted Kosan 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 Version 1 21 Computer Systems 36 77 in memory could we have the STA instruction also look at the number in the memory location that is just after it in memory to determine where to copy the contents of register A to The memory location immediately after the location that holds the STA instruction can contain the de
23. monitor and said Can we see some of the numbers that are in the memory locations in this computer We could I said but I have a better idea When I was a kid the first computer I had was a Commodore 64 and it was a wonderful machine for learning about computers I still have it and if you would like I will get it from the storage room set it up and we can play with it What do you think Sure said Pat I d love to see what an old computer looks like I retrieved the Commodore 64 http en wikipedia org wiki Commodore 64 from my storage room plugged it into a television and powered it up Within 5 seconds the following friendly blue screen appeared Pat said Hey that came up fast Our PC at home takes much longer to come up After reading the screen for a little bit Pat asked What is BASIC BASIC I replied is a typed language that a computer programmer uses to tell a computer what to do in a step by step manner It consists of a set of commands along with rules for how to use them For example if I type PRINT HELLO and then press the lt Enter gt key BASIC understands that I want it to print the word HELLO on the screen BASIC can also act like a calculator If I type PRINT 2 3 BASIC will add the numbers 2 and 3 together and give the result 5 Pat experimented by typing in a few more simple math operations then asked Can we tell BASIC to show us the numbers that are
24. not release the shackle until the correct combination is entered on the dial and the thing that the lock is attached to will not open until the shackle is removed from the hole it was put in Lets assume that the thing that the lock is attached to is a locker I said How does the locker know whether or not it has a lock attached to it Pat replied A person must first try to lift the locker s handle If there is not a lock in the handle s hole the handle will lift and the locker s door will open If there is a lock in the handle though the metal around the hole will bump against the metal of the shackle when the handle is lifted and this bumping will prevent the handle from lifting far enough to open the door That is correct I said One of the laws of physics states that two pieces of physical matter cannot occupy the same space at the same time The locker is a system that contains a lock as a subsystem and the lock uses this law of physics to inform the locker that it is not permitted to open This kind of physical informing or communication the bumping together of two pieces of physical matter is a common example of how information is used in a system Another bumping related example is the accelerator petal in an automobile If a driver wants to make a car go faster they press their foot against the accelerator petal the petal pushes against a lever the lever usually pulls on a cable that has some kind of
25. or Electrically Erasable Programmable Read Only Memory being developed in 1981 Instead of UV light being needed to erase these devices they could be erased and reprogrammed electronically one memory location at a time One of the more recent types of ROM memory chips is called Flash memory and it also can be reprogrammed electronically Unlike EEPROMs however Flash memory has to be reprogrammed in blocks of memory locations but since it is less expensive to make than EEPROM memory it has become very popular where large amounts of storage are needed Flash memory is not only used in personal computers it is also used as storage memory for digital audio players USB drives mobile phones and digital cameras T have an MP3 player said Pat if it has Flash ROM in it does this mean that the player has a computer in it There is a good chance that it does I said and if it has a computer in it then that computer is going to work in a similar manner to the models of a computer that we have been drawing on the whiteboards Once you understand how this model works you understand how most of the computers in the world work That is very powerful knowledge to have Amazing said Pat I feel like I am stepping into a whole new world I had never thought too much about computers before but now that I am starting to see how they work I want to know more about them after a pause Pat continued I am begin
26. programs as input Copyright 2007 by Ted Kosan 108 112 Version 1 21 Computer Systems 6 77 Right there on day one within 5 seconds of booting the 1980 era machine led the beginner directly and naturally to learning their first programming language Learning their first programming language is critical for a beginner because it gives invaluable insights into what a computer is and how it works The knowledge gained from learning that initial programming language makes it much easier to learn further programming languages It also opens doors for learning about all the other aspects of computers Another subtle benefit of the early 1980s era computers is that they guided the beginner into learning how to touch type because typing was the only way to communicate with these machines If you have observed an excellent programmer at work you can appreciate how valuable the skill of touch typing can be In contrast to the 1980s PC a typical modern PC provides a horrible educational experience for the beginner After unpacking the main unit and the monitor you have to plug in the power power cord figure out which of the 10 connectors on the back of the machine the monitor plugs into and plug it in without bending any of the little delicate pins Then you have to plug in the keyboard plug in the mouse and plug in the network connection or the phone line If you are lucky the machine has the operating system already installed on it
27. said between the cyberspace parts that are needed to make a computer a complete functioning system and the cyberspace parts that are added to this functioning system to make it do a given kind of work For example when you first turn on a typical personal computer it spends some time booting up which means loading the operating system into memory and running it and then you are presented with a graphical user interface or GUI This GUI allows you to do things like move a mouse pointer around on the screen select menus and look at the contents of a hard drive Your computer is now a complete functioning system but it has not been specialized for any given kind of work yet In order to do work you must select an application program with the mouse like a word processor and when this application is loaded and running the computer can then do specialized work with it The physical parts of a computer are called its hardware and the cyberspace parts of a computer including both the operating system and application programs is called software Computers Without Operating Systems Pat sat quietly for a few moments then said Earlier you said that most sophisticated computers have operating systems Are there some computers that do not have operating systems Yes I replied some smaller microcontrollers do not have a separate Copyright 2007 by Ted Kosan 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
28. should draw an arrow on both ends of a hard drive s cable because a computer can send information to a hard drive and it can also read information from a hard drive see Fig 18 Figure 18 Memory Map Inside Outside computer computer ROM XXX gt Keyboard ox gt Pe I P oe je gt Hard Drive T thought I was going to trick you with that question Pat I said but I was wrong I then drew arrows on both ends of the hard drive s cable to show that information can be sent both ways along it Loading An Operating System Now I said lets go back to discussing what happens when the CPU is Copyright 2007 by Ted Kosan 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 Version 1 21 Computer Systems 58 77 finished running the POST code and it needs to find more instructions to execute or it will lock up The remaining code in the ROM tells the CPU to talk to a storage device like a hard drive a Flash drive ora CDROM through the I O location that the storage device is attached to Actually in a real computer more than one I O location is used to talk to a storage device but for now a one I O location model is simpler to work with The CPU talks to a storage device and asks it if it has a program called an operating system stored on it If the storage device does have an operating system program stored on it the CPU reques
29. system at its other end that allows more air fuel mixture to enter the engine which results in the engine turning faster Moving back to the lock a human has the number sequence that will open the lock stored in their mind This number sequence represents information and the way that this information is communicated to the lock is by turning the lock s dial As the dial is turned bumping type information is communicated between the parts of the lock If the correct combination is entered the piece of matter that is informing the shackle that it cannot open is allowed to move freely and when the shackle is pulled this piece of matter moves away from the shackle as it is lifted and the lock opens Physical Parts Are Costly And Constrained Copyright 2007 by Ted Kosan 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 Version 1 21 Computer Systems 63 77 T am starting to see how information can be used as a part of a system Pat said but what does all of this have to do with computer operating systems and cyberspace I smiled and replied Parts made of physical matter have all kinds of constraints associated with them Pat If the parts are made of metal for example the ore for the metal has to be mined out of the Earth then the ore has to b
30. the top of the memory map then labeled the topmost rectangle ROM see Fig 15 Figure 15 Memory Map If ROM memories are read only how do the numbers get into them ROM in the first place asked Pat There are different kinds of ROM chips I said and there are CPU various ways that the numbers can be placed into them The earliest ROM chips had the numbers placed into them during the manufacturing process These ROMs are inexpensive to make but RAM the numbers that are placed into them can never be changed This means that if different numbers were needed in the area of memory that this type of ROM was in the old ROM chip would have to be removed and thrown away and a new ROM chip put in its place The need for ROMs to have the ability of having their numbers reprogrammed in the field which means where they are being used lead to the development of a chip called a PROM which is a Programmable Read Only Memory These chips had little patterns of fuses in them that would be burned when the devices were programmed They were more flexible than the early ROMs but the disadvantage of these chips was that they could only be programmed once The need to have a ROM that could be reprogrammed many times lead to the development of the EPROM which stands for Erasable Programmable Read Only Memory EPROMs can have programs placed into them by Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 49 77 any
31. to do step by step from the time you woke up in the morning until the time you went to sleep at night Your instructions might look something like this 1 Open your left eye 2 Open your right eye 3 Take your left hand and pull your covers down until they are below your feet 4 Turn your whole body 90 degrees so that your legs are hanging off the side of the bed 5 Place your left foot on the floor 6 Place your right foot on the floor 7 Raise your back 90 degrees so that you are sitting straight up 8 Put your left hand on the edge of the bed 9 Put your right hand on the edge of the bed 10 Push yourself up with your arms into a standing position As I said these instructions I acted some of them out and Pat began laughing You see I said this is pretty stupid Now imagine that your instructions were suppose to say turn left 45 degrees Walk forward 8 steps but instead they said turn right 180 degrees Walk forward 1000 steps These look like legitimate instructions but they are really garbage instructions because they told you to turn around and face your bed then walk forward 1000 steps A similar thing can happen with a computer Through a programming error a machine language instruction or data for an instruction can be placed into a program that does not mean anything in the context of the program This can cause the computer to attempt to do something just as Copyright 2007 b
32. ultimate way to obtain inexpensive used math 302 books so make good use of this resource too Never get rid of your math 303 books even after you have worked through them because you will want 304 to use them as a reference later Copyright 2007 by Ted Kosan 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 Version 1 21 Computer Systems 13 77 The Von Neumann Architecture Imagine that you were sitting at your PC working on a document and a friend came over to you pointed at the PC and asked What is in that box What would you say You might be tempted to throw some buzzwords http en wikipedia org wiki Buzzwords at them hoping that they would be satisfied and move on You could say That box is a computer and it contains the following items z CPU z RAM z ROM Hard drive m Flash drive m CDROM drive z Network card m Motherboard Most people however would not be content with this weak substitute for a true explanation and they would want to know what each of the above items did and how they all fit together At this point you are stuck You are going to have to set aside your work for awhile and try to explain how a computer works in a way that is as understandable as possible The fortunate thing is that the primary set of ideas upon which most computers are based are relatively simple Once you under
33. 007 by Ted Kosan 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 Version 1 21 Computer Systems 61 77 parts in a system can also be arranged into groups that form systems of their own and these smaller systems are often called subsystems The prefix sub means under so another way to think about a subsystem is as an undersystem Subsystems can contain subsystems of their own and many of the things in the world contain multiple levels of systems within systems A skyscraper s subsystems include its heating and cooling system lighting system telephone system elevator system and cleaning system which include janitors People can be part of a system asked Pat Yes I replied there are may kinds of systems that have people as parts A building s cleaning system fits our definition of a system because it has a goal to keep the building clean and it contains parts that interact together to attain this goal The mops dusters and garbage cans ina building are parts in its cleaning system but so are the janitors that interact with these parts T had never thought that people could be parts in a system said Pat but you are right they can There are many types of parts that can be used in a system I said including metal and pl
34. 07 by Ted Kosan 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 Version 1 21 Computer Systems 35 77 from a memory location to register A how about a store register A instruction to copy a number from register A to a memory location We can give it an opcode of say 141 I then started a new row in the Instruction Table and wrote a 141 in the opcode column Mnemonics That sounds good to me Pat said but if we come up with too many more instructions I am going to start forgetting which opcodes represent which operations That is a problem that the first computer programmers had too and the way they solved it was with mnemonics I said Neh moniks said Pat What s that Mnemonics I replied are aids that help people remember things that are difficult to remember One example is the color bands that are on the resistors you are going to sort tomorrow I said with a smile Each color represents a different number between 0 and 9 and the colors are Black Brown Red Orange Yellow Green Blue Violet Grey and White These colors can be remembered with the phrase Black Beetles Running On Your Grass Bring Very Good Weather A different type of mnemonic is the one that mechanics use to remember which way nuts and bolts tighten and loosen Righty tighty lefty
35. 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 Version 1 21 Computer Systems 40 77 The 6502 CPU s Instruction Set Pat looked at the mnemonic version of the small program we had written then asked How many instructions does the CPU in the Commodore 64 have The 6510 CPU that is in the Commodore 64 is based on the 6502 CPU and they both have 56 instructions I replied That may seem like a large number of instructions but most of them are as simple as the LDA ADC and STA instructions we have been working with Lets do an Internet search and find the complete list of instructions that the CPU in the Commodore 64 uses I did this and found the following list ADC ADd memory to accumulator with Carry AND AND memory with accumulator ASL Arithmetic Shift Left one bit BCC Branch on Carry Clear BCS Branch on Carry Set BEQ Branch on result EQual to zero BIT test BITs in accumulator with memory BMI Branch on result MInus BNE Branch on result Not Equal to zero BPL Branch on result PLus BRK force Break BVC Branch on oVerflow flag Clear BVS B
36. 2010 2011 2012 2013 Version 1 21 Computer Systems 68 77 operating system They usually just run one dedicated program and the cyberspace components that are needed to perform tasks that a separate operating system would perform are built into the program itself These microcontrollers usually run their dedicated program directly from ROM Some computers with operating systems such as cell phones and automotive computers will also run their operating system from ROM but computers like PCs and servers load their operating systems into RAM each time they are powered up Back To Loading An Operating System T understand now that an operating system is made using cyberspace parts said Pat but what does an operating system actually do We will talk about what an operating system does in a later discussion I replied but for now lets continue our discussion about what happens in a PC when the POST code in its BIOS ROM is nearly finished running and the last machine language instructions in the ROM tell the CPU to talk toa storage device in order to obtain the numbers that represent an operating system Do you remember how a CPU is able to communicate with devices that are outside of itself Pat looked at the model of a computer that we had been drawing on the whiteboard and replied A CPU is able to communicate with devices outside itself using the special I O memory locations in its memory map Yes I said
37. 5 1206 1207 1208 1209 1210 1211 Version 1 21 Computer Systems 43 77 interpreter reads the source code usually one line at a time determines what actions this line of source code is suppose to accomplish and then it performs these actions It then looks at the next line of source code underneath the one it just finished interpreting it determines what actions this next line of code wants done it does them and so on An example of an interpreter is the BASIC interpreter that is in the Commodore 64 When we typed in the line of BASIC code that asked the Commodore to print the contents of a memory location and pressed the Return key the Commodore s BASIC interpreter read the line we typed determined which memory location we wanted to see the contents of and then printed this number to the screen How many computer languages are there asked Pat Thousands of computer languages have been created since the 1940 s I replied but there are currently around 2 to 3 hundred historically important languages Lets see if we can find a list of them I brought up a browser on my PC did a search on computer languages and located a page that listed the historically important ones http en wikipedia org wiki Timeline of programming languages The Three Types Of Computer Memory Pat looked at the list of historically important computer languages for a while then asked Earlier you said that a com
38. I said while I fetched a couple of items from a cabinet I placed a CPU in Pat s left hand and I placed a simple calculator in the other hand I was careful to lightly touch Pat s left hand with my pinky finger before placing the CPU there O ONO RG O NN The CPU in your left hand is similar to the one that is in the Commodore 64 and it was widely used in the personal computers of the late 1970s and 1980s Its capabilities are similar to that of the calculator in your other hand in that they both can do simple mathematical operations on numbers and they both need to be told exactly what to do step by step by a human Told what to do said Pat I can t tell a calculator to do something it doesn t have any ears I laughed You are right you do not actually tell most calculators what to do not quite yet anyway but you do indicate to it what you want it to do How do you do this Pat looked at the calculator then said You tel it what you want it to do by Copyright 2007 by Ted Kosan 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 790 791 792 793 794 795 796 797 798 799 800 801 Version 1 21 Computer Systems 27 77 pressing its buttons Exactly I said Go ahead and tell the calculator that you want it to add the numbers 10 and 5 together and to give you their sum Pat typed 10 5 on the calculator What answer did you r
39. Version 1 21 Computer Systems 1 77 Computer Systems by Ted Kosan Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 2 17 Table of Contents The Golden Age of Personal ComputeTS 000 4 Computer Technologists Must Be Motivated Self LearnerTs 8 Learning How To Learn Technical Subjects 9 Learn even the uninteresting Parsts cccccccecssccsccscesccsceecesceececseaseneneees 10 Increase your capacity for reading as much as possible 10 Find a quite place to study and use it ooosoosononovvovononnonono noone 10 Minimize distraction Szalai KVA BA dalo o od dredu bo d a 11 Figure out what math is all about 00 000000e0eree 12 The Von Neumann Architecture sesesesersereresseseseserersrseseseoseseseseseserseseeo 13 How Does A Computer WOrk ccccceccecscsscsccscccecsesscncencecesceesscnseseceneecs 14 What Do The Numbers In Memory Locations Mean 22 Contextual MEGAN saa rn 23 What Provides The Context For The Numbers In A Computer s Memory 25 CPUs Calculators Without BUtLoTS sec cccececssisicitansanndangiagueeanmnidarsemadsaccccays 25 The Program Counter And The Instruction Register 28 Running A Machine Language Program 4 4 4 0 4000 29 WIE MONIC setrov DARA lk DZ bi o oo ooo aida eae 35 Machine Languages cerren ea ae
40. an 367 368 369 370 372 373 374 375 376 377 378 379 380 381 382 383 385 386 387 388 389 390 391 392 393 394 395 396 397 398 Version 1 21 Computer Systems 15 77 been buried under the moon s surface by someone or something What s a monolith and who or what buried it there Said Pat wondering where I was going with all of this A monolith is a vertical stone monument or marker I replied and in the movie aliens from a distant planet buried a monolith under the moon s surface waiting for the day when people from earth would be evolved enough to find it This rectangle I am drawing reminds me of the monolith from the movie because that monolith was also shaped like a tall vertical rectangle see Fig 1 That s eerie said Pat What is the monolith from 2001 a Space Odyssey doing in a computer I moved my head a little closer to Pat and in a hushed tone said elieve it or not a number of scientists have have said that one of the people who was on the team that invented the first modern computer in the late 1940s John Von Neumann was actually an alien from Mars What said Pat Oh come on Figure 1 You don t believe me I said in a hurt tone No said Pat That s ridiculous T ll make a bet with you I said If I am wrong I will give you a piece of junk electronic equipment from my storage room to take apart but
41. arm that is able to stretch for very long distances Instead 530 of walking from house to house the mail carrier sits in the post office 031 which is placed off to one side of the street and stretches the rubber arm to 532 each house Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 20 77 533 As I described this I drew a square off to the left side of the memory map to 534 represent the post office and then I erased an opening in the left side of 030 each memory location To show that the mail carrier can access all the 536 houses with that rubber arm I said I am placing an opening on the left 537 side of each of the memory locations the side that faces towards the post 538 office In a computer its post office is called a CPU which stands for 539 Central Processing Unit and another name for it is microprocessor 540 The CPU also has a small 541 number of memory sk Memory Map 542 locations in it some of 15 543 which are the same size 14 544 as the memory locations 545 that are in the memory 13 546 map These CPU memory CPU 12 547 locations can also hold a 11 548 number between 0 and Registers 549 255 but instead of being 10 550 given a unique address 72 9 551 number the memory 8 552 locations that are inside of 7 553 a CPU are usually labeled 554 with one or more letters 6 555 To distinguish them from 5 556 the memory locations that 4 557 are in the memory map 558 these m
42. astic parts rubber hoses water air electricity people and information It is this last kind of part information that I would like to focus on Information said Pat How can information be a part in a system if you can t even touch it Information is present in every system I said no matter what kind of system it is but sometimes it is not obvious how a system uses the information that is contained within it because information is not physical It cannot be seen or touched Lets take a simple system like a combination lock and see if we can determine how information is being used in this system I went to my storage room and returned with a combination lock What is the goal of this system Pat I said and I gave Pat the lock Pat studied the lock for a while turned the dial a few times pulled up on its shackle then said The goal of a combination lock is to prevent people from stealing your stuff Copyright 2007 by Ted Kosan 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 Version 1 21 Computer Systems 62 77 And how does it do this I asked Pat studied the lock some more then said The lock s shackle is placed through something that has a hole in it like a locker then the shackle is closed The lock will
43. at studied the microcontroller for a while then said Its so small Is there really a complete computer in this chip Yes I said and some microcontrollers are even smaller than that one Pat studied the chip a bit longer then gave it back to me I held the chip between my fingers and said If there is a program in this chip when it is turned on part of the chip enters cyberspace A computer program is what is used to create parts in cyberspace and by programming we will be able to create cyberspace lock parts and place them inside this microcontroller The microcontroller can be interfaced to the keypad and to the solenoid using the I O locations in its memory map It can then accept a combination from a human and open the lock if the combination is correct Is the cyberspace lock better than the normal lock Pat asked Copyright 2007 by Ted Kosan 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 Version 1 21 Computer Systems 66 77 In some ways it is I replied For example the combination cannot be changed in the normal lock but it can easily be changed in the cyberspace one The cyberspace lock can have additional numbers added to the combination with little effort and it can even keep track of how many times the lock was opened and a
44. at the CPU does is to look at the Program Counter to see what the address is of the next instruction to execute Our Program Counter contains the address 4 so it goes to memory location 4 and copies the number it finds there to the Instruction Register The number that is now in the Instruction Register is 141 and the CPU matches this number with the one in the Instruction Table to determine what operation it needs to do The operation description for the STA instruction tells the CPU to get the address of where it is going to store to from the Copyright 2007 by Ted Kosan 1025 1026 1027 1028 1029 1030 1031 1032 1033 Version 1 21 Figure 12 Run One Instruction Instruction Table Computer Systems 37 77 Memory Map a A A A NU RAR Ow CPU Registers 15 o co O ONO RG Oo N Mnemonic Opcode Operation Description LDA 169 Loads the number in the memory location immediately following the instruction s memory location into register A Adds the number that is in register A with the number in the memory location immediately ADC 105 i S d following the instruction s memory location The answer is placed into register A Stores the number in register A into a memory location The address of the memory location STA 141 D rae f f is represented by the number that is in the memory location just after the instruction next
45. bject you are studying is going to deeply interest you You might be tempted to skip these parts but unfortunately these uninteresting parts usually contain information that is necessary for fully comprehending the parts of the subject that do interest you It may not be pleasant but you have no choice but to force yourself to learn even the uninteresting parts of a subject A hidden benefit is that sometimes the material that interested you the least in the beginning turns into a passionate subject sometime later Increase your Capacity for reading as much as possible Until engineers create a way to plug a high speed network connection directly into your brain reading is the most concentrated means available for pumping deep detailed knowledge into your mind Take a few moments and think about all of the wonderful inventions that have been developed over the past 100 years From the automobile and airplane to radio television computers skyscrapers and satellites practically all inventions are the direct result of the inventor s ability to read and comprehend technical literature If you desire to become a computer technologist of some type you absolutely have to be a strong and continuous reader If you are already a strong reader but have not acquired the habit of reading technical literature then make an adjustment to your reading mix and start as soon as possible If you are not currently a strong reader make the resolution that th
46. but it can do millions of these operations every second A computer can do millions of operations a second said Pat Yes I replied which means that computers work in a much faster time frame than humans do Imagine that a computer can look at you from inside its screen It looks at you and what does it see If it is running millions of times faster than we are said Pat then we look like statues to it That is correct I said Imagine that this PC is watching me as I use my index finger to press the A key on the keyboard As I said this I started slowly moving my finger towards the A key From the computer s point of view it might take a hundred years for my finger to reach the top of the A key and another 5 years to press it down enough for the key to click At soon as the key clicks the letter A is quickly converted into a number this Copyright 2007 by Ted Kosan 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 Version 1 21 Computer Systems 76 77 number is encoded as electronic signals and these signals are sent into the computer at the speed of light The computer must get very bored said Pat while waiting for humans to interact with it I agree I said a computer usually spends thousands of years in its time frame waiting for humans to interact with it This also answers your quest
47. ce and quiet A monk will enter a small cell that has been carved in 259 the back of a cave and the opening is then sealed with bricks and mortar 260 Every day an attendant passes food and water to the monk through a 261 small hole in the wall but other than that they are completely alone for 262 perhaps 5 years at a time 263 If some Tibetan monks are able to mediate in a silent cave for 5 years 264 straight certainly you can work yourself up to quietly studying for an 265 hour or two at a time 266 Minimize distractions 267 To sacrifice means to surrender or give up something for the 268 attainment of some higher advantage or dearer object http miriams 269 well org Glossary 270 Certain occupations require greater amounts of focus effort and devotion 271 than others and most areas of computer technology fall into this category 272 It is an unpleasant but obvious fact that time spent doing a given activity 273 is time that cannot be spent doing another activity If the hours in a day 274 were unlimited then this would not be a problem Since this is not the 275 case however certain activities will need to be sacrificed on a daily basis 276 in order to devote that time to studying computers 277 What kind of activities might you want to sacrifice How about watching 278 television surfing the Internet talking to friends on the phone and the Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 12 77 279 big one
48. cite the letters of the alphabet over and over again The computer would say A B C D ina mechanical voice that sounded like a robot As students would come to my display I would point to each chip on the board explain what it did and I would end by saying this last chip allows the computer to talk About half Copyright 2007 by Ted Kosan 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 Version 1 21 Computer Systems 51 77 way through the day a group of students came to my table I went through my explanations and as I pointed at the speech chip a huge blue spark jumped from the end of my finger into the chip and it immediately went from saying A B C D to mumbling MWA BLA VLAZ DAUP That chip never did work correctly again Pat started laughing and so did I It wasn t very funny at the time I said but it certainly seems funny now Anyway that is an EPROM that you have in your hand and after they were invented in 1971 computer development in general moved forward at a guicker pace because of the shorter time it took to reprogram these devices Even though the EPROM was a very useful device it was still somewhat difficult to work with because it needed to be placed in a UV eraser before it could be reprogrammed This lead to the EEPROM
49. d the extra registers 1 849 in the CPU needed to run it Run One Instruction 0 850 should we go ahead and run it 851 to see what it does 852 Yes said Pat This is fun 853 Itis fun isn t it I said I am going to place a small button next to the 854 CPU label it Run One Instruction and when it is pressed the CPU will run 855 the instruction that the PC register is pointing to I drew a small 856 pushbutton switch next to the CPU then said Ready see Fig 7 857 Ready Pat replied 858 Okay I said lets go 859 I pushed the run button then said The first thing that the CPU does when 860 we tell it to execute the next instruction is to look at the Program Counter in 861 order to determine where in memory the instruction is located In this case 862 the Program Counter has the number 0 in it so the CPU which is like the 863 mail carrier with the long rubber arm goes to memory location 0 finds the 864 number 169 that is located there and copies it into the Instruction Copyright 2007 by Ted Kosan 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 Version 1 21 Computer Systems 30 77 Register As I say this I write the number 169 into the Instruction Register box in the CPU Figure 8 Memory Map The number 169 which is now in the Instruction Regi
50. e transported to a mill where it is transformed into metal shapes like rods and bars that are suitable for processing by machine tools These metal shapes then have to be transported to the manufacturing facilities that contain these machine tools so that the machines can create parts from them The parts are then transported to assembly facilities that assemble the parts into subsystems and these subsystems are often transported to yet other assembly facilities where they are assembled into final products Each step along the way from ore to finished product takes time and energy to accomplish and time and energy translate into cost Another kind of constraint that parts made from physical matter are under are the laws of physics These laws dictate that parts made from physical matter can be moved back and forth only so fast they can only handle so much force applied to them and there are limits to how large or small they can be Beyond this once the parts are formed into a given shape to serve a given function they cannot be easily reformed into other shapes to serve a different function For example if we wanted our combination lock to have a 4 number combination instead of a 3 number combination it would be extremely difficult to reshape all of the parts in the lock to accomplish this Moving Parts Into Cyberspace High cost and low flexibility are two of the main constraints that are associated with parts made of physical matt
51. eaning is a very powerful concept and it is what enables a computer s memory locations to reference any idea that a human can think of Each memory location can only hold a number between 0 and 255 but a human can have those numbers mean anything they wish Larger numbers than 255 can also be spread across more than one memory location What Provides The Context For The Numbers In A Computer s Memory I am beginning to understand contextual meaning said Pat but what provides the context for the numbers that are in a computer s memory locations When a program is loaded into a computer s memory locations I replied it is the program that provides the context The person who creates most of this context is the programmer that wrote the program When a programmer creates a program the ideas that are in a programmer s mind become linked to the numbers that represent the information that the program works with Each time the program is loaded into the computer s memory the program s numbers are loaded along with the ideas that are linked to these numbers Pat looked at the numbers on the Commodore 64 s screen a while longer and then went back to studying the model of a computer that I was drawing on the whiteboard Pat then said The CPU can copy a number from a memory location to a register and it can copy a number from a register to a memory location How does it know what numbers to copy where and what does it do w
52. eceive I asked 15 replied Pat Okay now look at the calculator and tell me what it is doing I said Perhaps 10 seconds went by then Pat said The calculator is not doing anything What are we waiting for Are you sure it is not doing anything I said No nothing said Pat am I missing something It does not look like the calculator is doing anything I replied but it is actually waiting for you to tell it what to do next Most calculators will wait for instructions from a human for a few minutes and if an instruction is not received during this time they will turn off in order to conserve battery power When a human turns a calculator on it will quickly enter a mode where it is waiting for instructions again Now tell the CPU in your other hand to add 10 5 I said Pat looked at the CPU turned it upside down then said I can t because there aren t any buttons No there are not any buttons on a CPU I replied so how does a human tell a CPU what to do I don t know said Pat and I can t even come up with a guess Lets go back to the model of a computer that we have been drawing on the whiteboard The CPU is sitting off to the side of the memory map and it is able to copy numbers from the memory map into its registers and from its registers to the memory map It does not have any buttons on it so a human cannot tell it what to do this way W
53. eing purchased and in the second example money was being borrowed from a friend What about the third example I said We were not doing anything special when you said Give me five and yet I knew exactly what you meant But I didn t just say Give me five in a calm voice like you did I said Give me 5 in a loud voice and put my hand out Everyone knows that when a person says Give me five in a loud voice and puts their hand out that they want you to slap it Yes I said everyone knows this because by saying Give me five in a loud voice and putting your hand out you provided what is called a context for the phrase Give me five Context means the circumstances within which an event happens or the environment within which something is placed In the first example the purchasing of the candy bars provided the context for Give me five and in the second example the borrowing of some money provided the context Contextual meaning therefore is the meaning that the context gives to the events or things that are placed within it T had never looked at things this way before said Pat but now that I think about it contextual meaning seems like it is used all the time Copyright 2007 by Ted Kosan 703 704 705 706 707 708 709 723 728 Version 1 21 Computer Systems 25 77 Yes I said most people use contextual meaning every day but they are not aware of it Contextual m
54. emory locations 3 559 are called registers and 2 560 our example computer has 1 561 a register which I am 0 562 going to label A 563 As I said this I drew a register in the CPU labeled it A and created an 564 opening on its right side to show that the carrier had access to its contents 565 Finally I placed a number between 0 and 255 into the register saying 566 Registers like memory locations must always contain a number in them 567 while the computer is running see Fig 5 568 The diagram was starting to take shape Pat studied it with great interest 569 then asked If the memory locations and registers can never be empty how 570 can the carrier remove numbers from them Copyright 2007 by Ted Kosan 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 Version 1 21 Computer Systems 21 77 I was wondering if you would notice that I said In a computer the numbers do not actually move The mail carrier is able to reach into any memory location and copy the number that is there into a register or copy a number from a register to a memory location but the original number is never moved When a number is copied to a register or memory location however the number that was already there is overwritten Pat looked up from the whiteboard to the PC s computer
55. er But what if it were possible to take the parts of a system that only consist of information and move them into cyberspace Move them into cyberspace Pat said Is this possible Yes Pat I replied Any part of any physical system that stores or communicates information can be moved into cyberspace using a computer As soon as a part is moved into cyberspace it becomes an idea and ideas existing in cyberspace are constrained much less by the laws of the physical world than their physical counterparts are Beyond this parts can be made in cyberspace that would be extremely difficult or even impossible to make Copyright 2007 by Ted Kosan 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 Version 1 21 Computer Systems 64 77 in the physical world Cyberspace parts can even be created assembled into systems disassembled and destroyed quicker than you can blink your eyes They can also be sent anywhere in the world through computer networks at the speed of light Pat s mouth dropped open in amazement Cyberspace does sound like a magical place Pat finally said but I don t fully understand how it works A Lock Made Of Physical Parts and Cyberspace Parts T do not think that anybody completely understands cyberspace yet Pat I said
56. es of information that expert authors with years of experience tend to forget are still fresh in their minds My first computer was a Commodore 64 http en wikipedia org wiki Commodore 64 and I took full advantage of the excellent educational materials that were available for it The User s manual for the Commodore 64 taught the beginner how to Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 5 77 program the BASIC programming language from scratch and the Commodore 64 s Programmer s Reference manual contained the machine s complete electrical schematics a description of each main chip s function specifications for all of the Input Output I O ports and explanations of its Central Processing Unit s CPU machine and assembly language At that time I thought the Commodore 64 was wonderfully complex and intriguing and it was not until much later that I realized how truly simple the Commodore 64 and its contemporaries were Most of the personal computers from that time had educational materials available similar to what the Commodore 64 had and I think this unique mix of inexpensive price relative simplicity excellent first generation educational materials and high community excitement level created the ideal conditions under which to learn how computers truly worked Many of the great software developers hardware engineers and hackers of today first learned how computers worked during the 1980s and it is my
57. es the computer its great power T will explain cyberspace more fully as we continue our discussion but lets use our current understanding of cyberspace to help us understand what a computer operating system is A computer operating system is a special kind of program that acts as a bridge between the physical world and cyberspace Most of the sophisticated computers in the world including PCs servers ATM machines car computers and cell phones have an operating system in them and it is the operating system in a device that enables it to access the resources of cyberspace Systems Within Systems We have been using the word system quite a bit for example computer system and operating system but what is a good definition of a system Before we continue lets find a definition for system on the Internet I went to my computer searched for a definition of the word system and found the following System A group of interacting interrelated or interdependent elements or parts that function together as a whole to accomplish a goal http www doe mass edu frameworks scitech 2001 resources glossary html This definition I said indicates that the purpose of a system is to accomplish a goal and that a system is made up of parts that work together to accomplish this goal Examples of systems include the water system that provides water to your home a skyscraper and an automobile engine The Copyright 2
58. essesesereseseeo 67 Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 3 77 Back To Loading An Operating SySteM cccccecssccsccscesccsceecesceecesceecaeees 68 Primary Storage And Secondary Storage cccccceccscceccsceceeseeeeeeeeeeeeeenes 69 General Purpose Computers Vs Specific Use ComputerTs 69 Running An Application Program ccesssscsssoscsscescasccecescescescabeasesscasescs 71 Something Is Missing From The Models 0000000 72 AOL ATB ON Te ESA ET OPT TET UMRMME EM MN a a 73 I Want To Learn More About Computer Software And Hardware 76 Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 4 77 The Golden Age of Personal Computers One morning teacher and I were troubleshooting an electrical malfunction on a friend s automobile Teacher I said When did you know what you wanted to be when you grew up Teacher pulled the oscilloscope probe away from the computer circuit it was probing smiled and said I have been grown up for a while now and I still do not know what I want to be I can remember however the day I had finally saved enough money to purchase my first computer I took it home set it up and within an hour I had written my first computer program At that point I laughed and thought I don t know what I want to be when I grow up but I am absolutely certain I want these wonderful machines to be a part of it
59. f the second CPU is a different model or in a different CPU family then no it wouldn t For example the assembly language for the 6510 CPU which is the CPU that the Commodore 64 contains will not run on an x86 family processor which most personal computers use Copyright 2007 by Ted Kosan 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 Version 1 21 Computer Systems 42 77 Low Level Languages And High Level Languages To get back to your question about how a computer can be programmed in machine language and in BASIC one has to understand that even though assembly language was easier to use than machine language it was still somewhat difficult for humans to develop programs with The early programmers wanted to develop programs in a language that was more like a human language English for example than the machine language that CPUs understand Both machine language and assembly language are considered to be Jow level languages because the thing that gives the numbers in these languages their contextual meaning is the CPU s hardware Programmers wanted to work with computer languages that have much of their contextual meaning derived from human languages so that the ideas that the programs worked with were more natural for humans to use They then fig
60. from one section of memory to another independent of the CPU Devices like hard drives graphic chips sound chips and network interfaces often use a DMA controller to copy numbers to and from other parts of memory in order to free the CPU to do other work This makes the overall computer system work faster There are other simplifications I have made during our discussion in order to present the core ideas of how a computer works as clearly as possible As we get deeper into how a computer works though I will add this more detailed information Something Is Missing From The Models The models of a computer that we have created on the whiteboard have enough detail to show the core ideas of how most computers in the world work As I said before in our modern computer based world this is extremely valuable knowledge to possess Furthermore as computers Copyright 2007 by Ted Kosan 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 Version 1 21 Computer Systems 73 77 become applied to increasingly more aspects of our society this knowledge will become even more valuable What do you think of these models of how a computer works I think its amazing said Pat The models explain so many things about a computer that I had no clue about before But somethin
61. g still seems to be missing Oh I said That is curious because the models are fairly accurate What do you think is missing It appears to me said Pat that the computer spends almost all of its time copying numbers from memory into the CPU copying numbers from the CPU into memory and doing simple mathematical operations Beyond this not much more seems to be happening No you are right Pat I said at its lowest levels a computer does not do much more than this But said Pat what about all of the cool things a computer can do Take a space game program for example A typical space game may have dozens of ships on the screen all shooting lasers and missiles at each other while avoiding all kinds of spinning asteroids and space junk Explosions and collisions are happening everywhere and the sounds from the ship s engines the lasers missiles collisions and explosions are being projected from the computer s speakers At the same time the game is taking all kinds of quickly typed input from the keyboard and it may also be in communication with one or more other computers playing the same game over a network How do these simple models of how a computer works explain all of the intense action that a game like this has Wink Of An Eye I was wondering if you would notice that some critical information was missing from the models I said and I will try to explain what it is There is a
62. hat would happen though if we were Copyright 2007 by Ted Kosan 802 803 804 805 806 807 808 809 810 811 812 813 814 815 817 818 819 820 821 822 823 824 825 826 827 828 829 Version 1 21 Computer Systems 28 77 to use the concept of contextual meaning to associate the equivalent of button presses with certain numbers and then placed these numbers into the memory map Could the CPU access these numbers Yes it could said Pat Instead of physical buttons numbers that represented buttons could be placed into memory and this would be just as good I continued Lets proceed by putting together a sequence of numbers representing button presses or instructions that will tell the CPU to add the numbers 10 and 5 together The first thing we are going to need is an instruction that copies a number from the memory map to a CPU register specifically register A Hmmm we have to pick a number between 0 and 255 to represent this instruction how about the number 169 That sounds as good as any number to me replied Pat I wrote the number 169 in memory location 0 on the whiteboard model then said In order to make it easy for the 169 load register A instruction to find the number it is suppose to load we will have it always copy the number that is one memory location higher in memory than the instruction itself I then wrote a number 10 into memory location 1 The Program C
63. hide their wanderlust which found its outlet in the Hungarian gypsy their language Hungarian is not related to any of the languages spoken in surrounding countries and their unearthly intelligence One had only to look around to see the evidence Teller Wigner Szilard Von Neumann Hungarians all Wigner had designed the first plutonium production reactors Szilard had been among the first to suggest that fission could be used to make a bomb Von Neumann had developed the digital computer Teller moody tireless and given to fits of laughter bursts of anger worked long hours and was impatient with what he felt to be the excessively slow advancement of Project Panda as the hydrogen bomb development was known Teller had a thick Martian accent He also had a sense of humor that could penetrate bone Pat s face slowly turned from skepticism to surprise while reading this passage When finished Pat looked at the tall rectangular monolith I had drawn on the board with a new sense of awe I said Sometime soon I will explain what resistors are and show you how to sort them but for now lets continue with our discussion Copyright 2007 by Ted Kosan 431 432 433 434 435 436 437 438 439 440 441 442 443 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 464 465 466 467 Version 1 21 Computer Systems 17 77 I picked up the marker and started drawing eve
64. in the Instruction Table and performs that 947 operation that is associated with this opcode The CPU then adds the 5 Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 34 77 948 which is in memory location 3 with the 10 that is in register A and then the 949 answer 15 is placed into register A The 10 that was already in register A is 950 overwritten I then erased the 10 that was in register A and replaced it 951 with a 15 see Fig 11 Memory Map Figure 11 a a NO RA oO CPU Registers 15 o co Run One Instruction O ON O R 0 O No Instruction Table Opcode Operation Description Loads the number in the memory location immediately following the instruction s 16 memory location into register A 105 Adds the number that is in register A with the number in the memory location immediately following the instruction s memory location The answer is placed into register A 952 Finally I said we need to update the Program Counter so that it contains 953 the address of the opcode of the next instruction to execute which will be 954 address 4 And I did this 955 What we need now I said is a third instruction that copies the number 956 that is in register A to a memory location so that we can use register A to do 957 other work Since we used a Joad register A instruction to copy a number Copyright 20
65. inter Memory Map Inside Outside Computes Compuier ROM XXX 4 Keyboard 5 Z emer ee 1 Figure 17 Pat looked at the model and said Lets see the CPU places a number that represents a capital letter A into the I O location that the printer is attached to this number is then converted into an electronic signal that represents the A and the electronic signal is sent to the printer The printer converts the electronic signal back into a number determines that it represents a capital letter A and then it prints it Very good Pat I said Finally which way should I point the arrow on the printer s cable Point the arrow towards the printer because information goes from the computer out to the printer Copyright 2007 by Ted Kosan 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 Version 1 21 Computer Systems 57 77 Correct I said and I drew an arrow on the printer s cable that pointed towards the printer Now Pat I think we know enough about how I O memory locations work to go back to the hard drive I drew another horizontal box underneath the box that represented the printer and wrote the words Hard Drive in it I then drew a line from the hard drive s rectangle to an unused I O location then I said which way should the arrow point on the hard drive s cable Pat thought about this for a moment then said You
66. ion about how computers are able to do all of the amazing things they do including games like your space game A computer screen is made up of little dots called picture elements or pixels for short The computer puts each ship asteroid laser and missle in your space game together pixel by pixel just like the Scalosians had to put their wall together brick by brick But the computer also has thousands of years in its time to do this From our point of view it appears that the computer is doing all of this work by magic I Want To Learn More About Computer Software And Hardware Pat sat quietly for a while then said I have enjoyed our discussion about how a computer works and now I really want to learn more about computer software and hardware You said that you would help me learn how to program so when can we start Come back soon I replied and we will begin TO DO Near line 1780 consider changing numbers to numerals and also bringing the numerals discussion from the emulator module to this module Another idea is to change the word hold to represent in reference to memory locations Version Author Description 1 0 TK Initial creation Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 77 17 Version Author Description Copyright 2007 by Ted Kosan
67. is is a skill you are going to begin to develop right now If deep technical literature is too much of a challenge to start with then pick an area of literature that interests you such as science fiction fantasy etc and start there Find a quite place to study and use it Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 11 77 243 This piece of advice cannot be stressed enough If you do not have a 244 quiet place to study you are never going to learn any technical 245 subject at a deep enough level in order to succeed Most technical 246 information is absorbed by the mind very slowly and it will require you to 247 study and restudy it during frequent blocks of quiet time measured in 248 hours in order for you to understand it 249 You may have to be very creative in order to solve this problem but solve 250 it you must If your house is not quiet during the day think about getting 251 up earlier to study or study later after everyone has gone to bed If you 252 have easy access to a public library or other quiet facility make use of it 253 If you have to go to a relative s or friend s house then do it 254 You may even have to resort to drastic measures like a garage a barn or 255 deep in the woods in order to find a quiet place to study Itis said that in 256 Tibet monks voluntarily allow themselves to be sealed in caves high up in 257 the Himalaya mountains for years at a time so that they can meditate in 258 pea
68. ith the numbers other than copy them CPUs Calculators Without Buttons I thought about this question for a few moments then said Lets start with the second part of your question first Many people who do not know very much about computers think of a CPU as a kind of brain In one way they are correct because it is the main place in a computer where operations can be performed on numbers But the only operations on numbers that most CPUs can perform are to add subtract multiply and divide them It can also compare the size of two numbers but most CPUs can not do too much more beyond these operations In truth a CPU is one of the dumbest things in the world In fact it is so dumb that it has to be Copyright 2007 by Ted Kosan 763 767 768 769 770 772 773 Version 1 21 Computer Systems 26 77 told exactly what to do Memory Map thousands of times a Figure 6 second 15 14 13 12 11 10 It sounds to me like a CPU is not much more than a calculator said Pat CPU Registers That is an excellent observation Pat I said a CPU 72 is not much more than a simple calculator the kind that can only add subtract multiply and divide I then drew the symbols for addition subtraction multiplication and division in the CPU box on the whiteboard see Fig 6 There is a significant difference between a CPU and a calculator though Put out both of you hands palm up Pat
69. learning Teacher looked at me cocked an eyebrow paused and then grabbed me by the back of the neck and pushed my head under the water Teacher s reaction surprised me so much that I did not have time to take a deep breath before hitting the water and I was soon struggling Teacher finally pulled me up and after I had recovered somewhat asked me what the thing I wanted most was when I was under the water Air I replied The only thing I wanted was Air Teacher then said In order for your learning to be effective you must want to learn the thing you are learning as much as you wanted air when your head was under the water That which is learned without desire is soon forgotten That which is learned with great desire however is knowledge that will be remembered forever Computer Technologists Must Be Motivated Self Learners When I was a senior in High School in 1982 inexpensive personal computers were so new that our school only had a few and none of the teachers in the school knew how to program them Since none of the teachers knew how to program these computers no programming classes were offered If we wanted to learn about these machines we had to do so on our own While some schools in the world did have classes on programming many did not and even the ones that did were not very in depth At the time I thought I was very unfortunate to be in a school that did not have classes
70. map If it took 1 second to count each of these memory locations it would take you over 30 years to count them all A billion memory locations cried Pat Thats a lot of numbers How does a computer keep track of which numbers are in which memory locations That is an excellent question I said One certainly could not give them their own names like Bill or Lisa or Tom because one would run out of names long before running out of memory locations Even the early computers had too many memory locations to give each location its own name and therefore the inventors of the modern computer had to solve this problem right from the start How do you think they did it Perhaps if you think of some examples in the physical world that have a similar problem a lot of items that need to be uniquely identified that may help Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 19 77 497 Pat looked out of the window for a while trying to think of something in the 498 physical world that was similar to the memory locations Across the street a 499 dog was barking at the mail carrier who was delivering mail and Pat 200 watched the carrier place letters into one mail box and then another 501 I got it cried Pat those memory locations are similar to house addresses Memory Map 202 All of the houses on this street have their own address 503 and the houses on my street are the same way Did the 504 inventors
71. memory location after the instruction itself The CPU looks in this location which is location 5 and finds an 8 there Finally the CPU copies the number which is currently in register A which is 15 our answer to memory location 8 Pat then picked up the marker and wrote a 15 in memory location 8 Very good Pat I said but you need to do one more thing before the instruction is finished Pat looked at the whiteboard for a few moments and then said Oops I forgot to update the Program Counter Pat then erased the number that Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 38 77 1034 was in the program counter and wrote a 6 there see Fig 13 Memory Map Figure 13 Ss M A A NU R a CPU Registers 15 a o co Run One Instruction O M O RG O N Instruction Table Mnemonic Opcode Operation Description Loads the number in the memory location immediately following the instruction s memory location into register A LDA 169 Adds the number that is in register A with the number in the memory location immediately ADC 105 me following the instruction s memory location The answer is placed into register A STA 141 Stores the number in register A into a memory location The address of the memory location is represented by the number that is in the memory location just after the instruction
72. n episode from the original Star Trek TV show called Wink of an Eye that can help explain the missing piece In this episode the Enterprise is exploring an outer part of the galaxy when it receives a distress call from a nearby planet The ship is placed into orbit around the planet and a landing party consisting of captain Kirk Mr Spock Dr McCoy and some red shirted crew members is beamed down to the planet There are buildings and other signs of civilization on the planet but no humans can be found Copyright 2007 by Ted Kosan 2164 2165 2166 2167 2168 2169 2192 2194 2195 2196 2197 Version 1 21 Computer Systems 74 77 and the landing party s instruments can not even detect any animal life They keep hearing insect buzzing sounds though which is strange because there are no insects Have you ever watched any of the original Star Trek episodes Pat Sure said Pat I have seen a number of them Do you know what usually happens to red shirted crew members I asked Something bad usually happens to them Pat said Right I said something bad usually happens to them and this episode is no exception Soon after beaming down to the planet something bad happens to one of the red shirted crew members In this episode the people that had sent the distress signal who are called Scalosians are still on the planet but their metabolisms have been vastly increased by radiation which was emitted from a
73. nds for Random Access Memory but a better name for it would have been RWM or Read Write Memory because numbers CPU can be both copied into this kind of memory and copied out of it All the numbers in RAM memory locations will keep whatever numbers they hold as long as the computer is on but when the RAM computer is turned off all the numbers in all RAM memory locations are lost Memory that looses the numbers it contains when the power it turned off is called volatile memory As I said this I drew a horizontal line across the middle of the memory map and then label the bottom half of the rectangle RAM In this new model of a computer I am having the bottom half of the memory map represent RAM memory locations In a PC there are millions of RAM memory locations which is too many to show in this model Instead of drawing all of the RAM locations individually I am representing them with this rectangle labeled RAM see Fig 14 As long as a computer is powered up I continued every memory location will always contain a number between 0 and 255 There is no such thing as a blank memory location when the power is on When the power is off however all of the RAM memory locations are blank When the computer is Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 45 77 first turned on each RAM memory location has a number between 0 and 255 randomly appear in it during the time that the system s power rises to it
74. ning to understand how numbers can be placed into the various ROM memories What I want to know now is what the numbers Copyright 2007 by Ted Kosan 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 Version 1 21 Computer Systems 52 77 usually mean that are put into these ROMs BIOS And POST Lets go back then I said to the question I asked you about what happens when a computer first powers up I asked If all the RAM memory locations in a computer come up with garbage numbers in them where in memory does the CPU go to get its first instructions when it first powers up We determined that some type of ROM chip needs to be placed into the section of memory that contains the address that a CPU first goes to when it is turned on A machine language program is placed into this ROM chip and the machine language program usually tells the CPU to check the various parts of the computer system to make sure they are operating correctly On a typical PC the ROM that is placed in the part of memory that the CPU first looks at for its initial instructions is called the BIOS or Basic Input Output System The part of a PC s BIOS that tells the CPU to check the computer system for correct operation is called the POST or Power On Self Test code When you first turn on you
75. nly spaced horizontal lines across the rectangle starting from its bottom and working my way towards the top One of the primary things that computers have in them are a bunch of boxes all lined up next to one another Each box is the same size as all the other boxes and just like normal boxes these boxes hold something But you cannot go into a computer open the tops of these boxes turn the computer over and expect things like paper clips or marbles to fall out see Fig 2 These boxes are very special They cannot hold physical objects and yet they can contain anything a human mind can think of This is a paradox that I will try to explain in a little while but for now if these boxes do not hold physical objects can you guess what they do contain Pat thought for a little while and then said I read somewhere that computers are good at something called crunching numbers so I guess these boxes have something to do with numbers Figure 2 I smiled and said Very good Each of these boxes can hold a number and that is all they can hold There must be something very special about numbers if the main purpose of these boxes is to hold them The way that a computer uses numbers is one of the main sources of its incredible power and it seems fitting that John Von Neumann one of the greatest mathematicians of all time had a hand in placing them there The boxes in most computers can each hold a number between 0
76. ocations in a computer come up with garbage numbers in them where in memory does the CPU go to get its first instructions when it first powers up Hmmm said Pat while looking at the memory map It can t get its first instructions from RAM because RAM contains garbage data in it right after it powers up It seems that we need a kind of memory that remembers its numbers even when the power is off You had said that there are three basic types of memory in a memory map does one of the other two types work like this ROM Read Only Memory Yes I said very good One of the other two types of memory in a memory map is called ROM memory and it stands for Read Only Memory Another Copyright 2007 by Ted Kosan 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 Version 1 21 Computer Systems 48 77 name for this memory is non volatile memory The name ROM fits this type of memory a little better than RAM s name does because the numbers in this second type of memory are meant to mostly be copied or read from The special thing about ROM memory is that after numbers have been placed into it they will be held there even after the power is turned off As I was saying this I drew a second horizontal line about one eighth of the way down from
77. of the computer give each memory location 19 505 its own address 14 13 506 Yes I said You figured it out Each memory 12 507 location has its own unique address and all computers 508 give the first memory location an address of 0 the next 11 509 memory locations receives an address of 1 and so on 10 510 all the way to the top of the memory map As I said 9 511 this I started placing an address next to each of the 8 912 memory locations starting at the bottom of the memory 513 map and working up At the top of the rectangle I 7 514 wrote the words Memory Map see Fig 4 6 515 One way to think of a memory map is that it is a very 516 long street with thousands and thousands of houses on 4 517 it each house or memory location can hold a number 3 518 between 0 and 255 and each house has its own 2 519 address 1 520 Pat thought about the mail carrier then said Physical 0 521 houses have mail carriers that deliver mail to them and 522 retrieve mail from them If memory locations are like 523 houses what delivers and picks up the numbers from 524 the memory locations Figure 4 525 That is another good question I said You can think of a computer as a 926 strange kind of world with one long street on it that only has one mail 527 carrier Instead of letters and packages this mail carrier can only deliver 528 and retrieve numbers Another remarkable thing is that this mail carrier 529 has one rubber
78. ograms are large or if more then one program is going to be running on the computer at the same time then the amount of RAM needs to be large If one has many programs or the amount of data the programs use is large then the amount of secondary storage needs to be large The more general purpose a computer needs to be the more RAM and secondary storage it needs Does a general purpose computer also need a large about of ROM Pat asked No I replied a general purpose computer only needs enough ROM to hold instructions that test the hardware during power up instructions that allow the operating system to more easily talk to the hardware data that configures the motherboard and instructions that help load the operating system into RAM In a general purpose computer the amount of ROM in its memory map is significantly less than the amount of RAM Specific purpose computers on the other hand usually have significantly more ROM than What is a specific purpose computer asked Pat and why do they have more ROM than RAM A specific purpose computer is a computer that has been designed to perform one dedicated task Examples of specific purpose computers include computers that control automobile engines televisions DVD players heating and cooling systems audio systems elevators and security systems The reason that specific purpose computers usually have more ROM than RAM is that they typically only run one
79. ogress in the twenty first century it will be more like 20 000 years of progress at today s rate The implications of this passage are that technology is changing so quickly that it is becoming impossible for teachers to learn the new knowledge fast enough to then pass it on to their students Therefore like it or not if you have the desire to become a computer technologist then you have no choice but to become a self motivated learner yourself Learning How To Learn Technical Subjects Many of the technical books I have read in my life include a message in the preface of the book that informs the student that if they do not read the book carefully do the assigned problems ask questions and generally get actively involved they will not learn the subject material I have Copyright 2007 by Ted Kosan 208 209 210 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 Version 1 21 Computer Systems 10 77 found this advice to be very true and I recommend that you follow it In addition to this sound advice however I am going to add some more thoughts of my own that you may find helpful Learn even the uninteresting parts In an earlier section we already addressed the fact that learning without desire is not very effective What little is learned it usually retained only long enough to pass a test and then it is quickly forgotten The problem here is that not every part of a su
80. on computers but I was to eventually find out that this misfortune was actually a wonderful blessing in disguise I think that this blessing was one of the significant benefits that the golden age of personal computers provided for the people who learned about computers during that time Since I could not take a class on computers at school I would go home at night and sit in my bedroom and look at my computer There I was there was the computer and next to it on the desk were the computer s User s manual and its 2 inch think Reference manual I looked at the computer looked at the User s manual then looked at the Reference manual There was nobody to teach me about the computer There was nobody to ask questions to about the computer And it was so utterly quiet Finally for the first time in my life I picked up a technical book the User s manual and I started to actually read it Nobody had told me to do this Nobody had assigned this work for me to do and nobody was going to test me over what I had read I started reading the book because I Copyright 2007 by Ted Kosan 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 192 193 194 195 196 197 198 199 200 201 202 203 204 206 207 Version 1 21 Computer Systems 9 77 desperately wanted to learn how to use my computer and reading the book was the only way I had to do this After reading the first few pages of
81. one having a device called an EPROM programmer What is even more interesting is that these chips have a small round window on their top that allows light to shine into them If ultra violet or UV light is shined into this window for perhaps 10 minutes the numbers that were last programmed into the chip are erased by this light Aside from their use as ROMs EPROMs are a very interesting kind of computer chip to have because they allow people to see what the inside of a chip looks like I have some old EPROMs around here somewhere would you like me to give you one Yes please said Pat So I searched through my collection of electronic parts until I found an EPROM which I then gave to Pat As I handed Pat the EPROM chip I was again careful to lightly touch Pat s hand with my pinky before I placed the chip into it ESD Electro Static Discharge Why do you keep touching my hand with your pinky finger before you give me a chip Pat asked I replied Have you ever walked across a carpeted room during the Winter reached out your hand to open a door and then received a shock of static electricity from the metal door knob Oh yes answered Pat Sometimes I have even seen a blue spark jump between my hand an the door knob and those shocks really hurt Believe it or not I said little sparks like that often move between your fingers and the things you touch even if you cannot feel them Anothe
82. opinion that the unique conditions existing at that time enabled them to gain the deep understanding of computers that is the core of their success today That Golden Age of computers occurred a while ago however and an amazing amount has changed since then The changes include personal computers that are orders of magnitude faster than the PCs of the early 1980s the Internet the World Wide Web Cell Phones and enormous amounts of educational materials on computers and computing that is expanding at an increasing rate There is more of everything in the world of computers now than was available in the 1980s but unfortunately this more of everything in computing that we have now provides an unfriendly environment within which to learn about computers if you are a beginner Here an example of what I mean When I purchased my Commodore 64 I brought it home attached it to my television it did not need a special monitor applied power to it and waited the 5 seconds it took to boot The operating system was stored in the system s main board so it did not have to load from an external storage device The keyboard was built into the computer itself so the only wires that needed to be attached were the power cord and the cable that went to the television The main screen actually the only screen consisted of a command line interface that waited to accept BASIC Beginner s All Purpose Symbolic Instruction Code language commands and
83. ounter And The Instruction Register Now we have a couple more problems to solve before we can proceed The CPU is going to need to know where in memory to find the current instruction and it is going to have to have a place to copy it to in the CPU before it can use it The way that most CPUs solve the first problem is with a special register called a Program Counter or Instruction Pointer The Program Counter holds the memory address of the current instruction I drew a register box underneath the A register and labeled it PC I then wrote the address 0 in this register and drew an arm with a hand on the end of it from the right side of the Program Counter to memory location 0 Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 29 77 830 The second problem is solved Figure 7 Memory Ma 831 with another register called igure ry Map 832 the Instruction Register and it 15 833 is the register that the number 14 834 that represents the current 13 835 instruction is copied to inside 836 the CPU I drew another box CPU 12 837 in the CPU underneath the 11 838 program counter register and Registers 10 839 labeled it IR The last thing I 9 840 did was to place X s in all of 841 the memory locations that we 8 842 were not focusing on at the 7 843 moment 6 844 Running A Machine 2 845 Language Program 4 846 Now that we have written the 3 847 first part of our small program 2 848 and place
84. piled program can be stored for later use I know that a computer usually stores programs on its hard drive but where does something like a hard drive fit into this model of a computer that is on the whiteboard Now that we have gone through the work of figuring out how a computer operates at its lowest levels I replied it is easier to explain how devices like hard drives are attached to one Instead of using the detailed model of a computer that we have developed on this whiteboard though I am going to draw a similar diagram that is more general I picked up a blanc whiteboard and started whistling the theme to 2001 A Space Odyssey again as I drew another memory map Instead of drawing the individual memory locations however I left the memory map unfilled but still labeled it memory map at the top I also drew an empty square to the left of the memory map and labeled it CPU Copyright 2007 by Ted Kosan 1268 1271 Version 1 21 Computer Systems 44 77 RAM Random Access Memory I then asked Pat What does the word RAM mean to you Pat thought for a few moments then replied I think RAM has something to do with how much memory a computer has I know that my Mom s computer did not have enough RAM to run a new program she bought so she had a friend add more RAM to it That is correct I said RAM is Figure 14 Memory Map one of three types of memory that can be present in a memory map RAM sta
85. piled programs consist of numbers that represent machine language instructions and from what I know the programs that a PC can run are stored on its hard drive My guess is that the CPU can get the machine language instructions it needs from the programs on its hard drive You are right I said After it has finished running its POST code A PC usually obtains the machine language instructions it needs from its hard drive But how does the PC s CPU talk to a hard drive We have not placed a hard drive into our whiteboard model of a computer yet where do you think it should go I O Memory Pat looked at the whiteboard model while thinking about this then said I am not sure where it should go Earlier though you said that there were 3 kinds of memory in a computer and we have only talked about two of them which are RAM and ROM Maybe the hard drive is attached to this third kind of memory Copyright 2007 by Ted Kosan 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 Version 1 21 Computer Systems 54 77 That is a good guess I said the hard drive in a computer is attached to the third kind of memory As I said this I pointed at the whiteboard to the the area of the memory that was between the ROM memory and the RAM memory As with
86. program or a small number of programs This program or programs along with perhaps a small operating system take up a comparatively small amount of space which can usually fit into ROM primary storage Microcontrollers are the kind of computer system that are most widely used as specific purpose computers Copyright 2007 by Ted Kosan 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 Version 1 21 Computer Systems 71 77 That makes sense said Pat Maybe tonight I will ask my Mom if I can take her car computer apart so that I can see how much ROM and RAM it has We both laughed at this T would not do that on a running car if I were you I said at least not until you have learned how to do some computer interfacing In the mean time I have some old cars in my recycle yard that have engine computers in them You are welcome to take one of those computers apart if you would like Thanks said Pat I think I will do that soon Running An Application Program Lets continue our discussion of what happens when a PC boots up I said We made it to the point where the operating system was loaded into RAM and was presenting a GUI or command line interface to the user Can you use the model on the whiteboard to describe what happens when the user runs an application program
87. r name for these sparks is ESD or Electro Static Discharge and it is caused by static electricity Most of the time ESD sparks do not cause any harm but if you allow sparks like that to hit a computer chip the chip can easily be damaged I have a couple of stories about ESD and computer chips that you may find interesting The first story happened when I was younger and working for a company called Tire Tele as an electronics technician Tire Tele manufactured low Copyright 2007 by Ted Kosan 1474 1475 1476 1477 1478 1479 1480 1481 Version 1 21 Computer Systems 50 77 tire pressure warning systems for automobiles and these systems consisted of sensor units which were placed inside each tire of an automobile and a receiver which was placed on the dash board The sensor units would periodically send pressure information to the receiver and if any of the tires was loosing pressure the receiver would alert the driver Tire Tele began selling their product to people and everything was going fine Then about 6 months after the first units were sold they started to fail and people began returning them for repair or for a refund The Tire Tele engineers determined that the computer chips in these devices were failing and so they sent a few of the dead chips back to the chip manufacturer for analysis The chip manufacturer disassembled the chips looked at them under a high power microscope and discovered that the little
88. r PC Pat what kinds of things do you notice Well said Pat the first thing that happens is that the screen flashes on and changing numbers are then shown at the upper left of the screen After this the lights on my keyboard blink my hard drive starts making noise and then a little later my graphic desktop is shown These are all a result of the machine language POST code telling your CPU to check each of these devices I said The changing numbers are shown as the CPU checks the system s RAM chips the keyboard lights are blinked when it is checked and the hard drive makes noise when it is checked There are many more devices in the PC that the POST code also checks but these do not make noise nor do they flash lights or print to the screen This should answer your question about the meaning of the numbers that are typically placed into ROM memory A significant amount of these numbers represent a machine language program that tests the computer system when it is first turned on Other parts of the same ROM also usually contain machine language code that controls various pieces of hardware that are attached to the system We will talk about this other kind of code later For now we have another a more pressing problem The amount of ROM Copyright 2007 by Ted Kosan 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575
89. ranch on oVerflow flag Set C CLear Carry flag CLD CLear Decimal mode CLI CLear Interrupt disable flag CLV CLear oVerflow flag CMP CoMPare memory and accumulator CPX ComPare memory and index X CPY ComPare memory and index Y DEC DECrement memory by one DEX DEcrement register S by one DEY DEcrement register Y by one FOR Exclusive OR memory with accumulator INC INCrement memory by one INX INcrement register X by one INY INcrement register Y by one JMP JuMP to new memory location JSR Jump to SubRoutine DA oaD Accumulator from memory DX oaD X register from memory DY oaD Y register from memory SR ogical Shift Right one bit NOP No OPeration ORA OR memory with Accumulator PHA PusH Accumulator on stack Copyright 2007 by Ted Kosan 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 Version 1 21 Computer Systems 41 77 PHP PusH Processor status on stack PLA PuLl Accumulator from stack PLP PuLl Processor status from stack ROL Rotate Left one bit ROR ROtate Right one bit ReTurn from Interrupt ReTurn from Subroutine SuBtract with Carry SEt Carry flag Et Decimal mode Et Interrupt disable flag Tore Accumulator in memory Tore Register X in memory Tore Register Y in memory TAX T
90. ransfer Accumulator to register X TAY Transfer Accumulator to register Y TSX Transfer Stack pointer to register X TXA Transfer register X to Accumulator TXS Transfer register X to Stack pointer TYA Transfer register Y to Accumulator U U U U U Look at all of those instructions said Pat That would sure take a lot of time to look up the opcodes for all of them after the mnemonic version of a program was finished Hmmm couldn t the mnemonic version of a program be given to the computer so that it could do the opcode lookup automatically Yes it could I replied and this is what the early programmers thought of too The type of program they developed to do this is called an assembler and what it does is take the mnemonic version of a program and convert it into its machine language equivalent The name they then gave the mnemonic version of a program is assembly language and it is the source code that the assembler takes as its input information Very few programmers develop programs in machine language today but a number still write programs in assembly language Will the machine language for one CPU run on another CPU Pat asked That depends on a number of things that we will not get into now but the short answer is that if the second CPU is the same model or in the same family as the first CPU then it would I
91. rating system starts to run The process of copying the operating system s numbers from a storage device into RAM and running the core of the operating system after it has been loaded is called booting the computer system Assuming that this is a model of PC the operating system will show a GUI or a command line interface like the Commodore 64 has to the user when it is finished booting and it is then ready to run applications Primary Storage And Secondary Storage The purpose of a storage device is to hold numbers Pat asked Yes I replied The amount of RAM and ROM in a computer s memory map is limited and as we talked about earlier when the power on the computer is turned off the numbers in the RAM memory locations disappear Therefore in order for a computer like a PC or a server to be useful it must have the ability to hold numbers outside its memory map for later use The storage that is in a computer s memory map is called primary storage and the storage that is held in devices outside of the computer is called secondary storage or mass storage Examples of secondary storage devices include hard drives flash drives CDROMs DVDs and magnetic tapes To give you a feel for the amount of primary vs secondary storage in a typical PC we can take this PC on the table as an example This PC has 1 gigabyte of RAM and 100 gigabytes of hard drive space That s a big difference said Pat but if the hard d
92. re challenging than the beginner did in the early 1980s The task is more challenging but then again the returns on one s investment of labor are significantly greater too Computer technologies have moved into almost all aspects of society and their growth continues to expand at an increasing rate However for those who are willing to discipline themselves focus their efforts and invest the hard work it takes to master the fundamentals of computer technology the rewards are well worth the effort The Golden Age of personal computers is part of the past now and the unique environment it provided for deep natural learning of computer fundamentals is part of the past too While I can not bring that age back I did live through it and I think I can pass some of that age s magic along to you if you are willing to work hard to learn the information that I am going to be guiding you through in this document You see one of the secrets of success that age taught us was not what we learned but rather the way we learned it Copyright 2007 by Ted Kosan 132 133 134 135 136 137 138 139 140 141 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 Version 1 21 Computer Systems 8 77 One summer afternoon Teacher and I were installing a sonar system on a boat at the lake Teacher I said What is the secret to effectiv
93. rive can hold so many more bytes than the RAM can why not just get rid of the RAM and use the hard drive s storage instead That is a good question Pat I said The reason that secondary storage can not be used in place of primary storage is that primary storage like RAM is able to have numbers copied into and out of it much faster than secondary storage can Primary storage is faster than secondary storage but it is also more expensive per byte Both types of storage are needed however in a general purpose computer like a PC General Purpose Computers Vs Specific Use Computers Copyright 2007 by Ted Kosan 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 Version 1 21 Computer Systems 70 77 A PC is a general purpose computer Pat asked Why is that General purpose computers I replied are designed to maximize their flexibility so that they can be configured as needed to perform various kinds of work The way that a computer is configured to perform a given kind of work is with a program Examples of programs that allow a computer to do a given kind of work include word processors games browsers and media players Since a PC can easily run numerous kinds of programs it is considered to be a general purpose computer If the pr
94. rld that are made more capable and flexible by having some of their parts exist in cyberspace including automobiles televisions aircraft microwave ovens heating and cooling systems machine tools and telephones As we move into the future traditional physical systems of all kinds are being redesigned to include cyberspace parts and systems that already have cyberspace parts are being redesigned to increase their percentage of cyberspace parts One might even imagine that all systems would be made 100 of cyberspace parts if it were possible Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 67 77 Pat thought about this for a while then asked What type systems today have the greatest percentage of cyberspace parts I smiled and said The type of systems that currently have the greatest percentage of cyberspace parts are sophisticated computers like PCs and servers Usually over half of a sophisticated computer system is built from cyberspace parts and the portion of a computer that is built from cyberspace parts is called its operating system That s what an operating system is cried Pat The portion of a computer that is made from cyberspace parts Yes I replied this is one way to look at it Application Programs What about applications programs that run on a computer like a word processor asked Pat arent those part of the computer too Tam making a distinction I
95. s operating level Since these RAM memory locations come up with random numbers in them there is no contextual meaning associated with these numbers so they do not hold any meaningful information Computer programmers sometimes say that memory locations that do not have any contextual meaning associated with them contain garbage After a computer has gone through its power up cycle its RAM memory locations are ready to have numbers copied into these locations that have contextual meaning associated with them The numbers that represent machine language programs have contextual meaning associated with them and an example of this was the small machine language program we developed a little while ago But now we have a problem I said because when the power up cycle on a computer is finished a small electronic circuit senses this then sends a signal to the CPU that says the power is on now start running Most CPUs have an address built into them at the factory which is the address in the memory map where they should look for their first machine language instruction immediately after power up In the Commodore 64 this address is 65532 If a machine language instruction has not been purposefully placed into this memory location the computer will lock up and everyone has had a lot of experience with their computers locking up Pat laughed and said Oh yes My computer locks up all the time I smiled and continued
96. stand these ideas and how they interact with each other you will be able to look at almost any computer from the computer that controls a car s engine to the computer that runs your cell phone up through the computers that run the Internet and you will understand how it works The following is my explanation of how a computer works as given to an imaginary young friend of mine called Pat Copyright 2007 by Ted Kosan 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 Version 1 21 Computer Systems 14 77 How Does A Computer Work How does a computer work Pat asked one day while visiting me at my shop I have had a computer since I was a kid all my friends have computers and my parents have two of them but computers seem like magic to me because I do not really understand them I smiled and replied In a way Pat computers are magic because part of a computer exists in the physical world and the other part exists in a non physical realm called cyberspace Cyberspace asked Pat What is cyberspace and where is it Where is cyberspace I said Cyberspace is everywhere and nowhere Each time you surf the Internet on your computer you enter cyberspace but you also enter it when you make a telephone call or play a video game As for what cyberspace is this wo
97. ster represents an instruction or operation that the CPU must perform In this case the number 169 instruction means go to the next memory location immediately after the one that held this instruction and copy the number that is there into the A register see Fig 8 Registers XXX In order for the CPU to determine what a given instruction should do it must have the eguivalent of a map or table that associates the instruction s number with the actions that should be performed when this instruction is run I said Below the CPU I drew a rectangle and labeled it Instruction Table Towards the top of this rectangle I wrote the number 169 followed by the sentence Loads the number in the memory location immediately following the instruction s memory location into register A Run One Instruction O 1 M U RG O N OC In this case the CPU looks at the number 169 which is in the Instruction Register I said matches this number in the Instruction Table and then performs the operation that has been associated with this number The contents of the next memory location after the one that holds the instruction is then copied to register A I erased the old value that was in register A and replaced it with the number 10 see Fig 9 Copyright 2007 by Ted Kosan 898 899 900 901 902 903 904 905 906 907 908 909 Version 1 21 Computer Systems 31 77 Memory Map Figure 9
98. stination address that it needs I blinked and then stared at Pat fora few moments Uhh yes Pat thatisa very good idea I finally said in fact most CPUs use the technique you just described in their store instructions Are you sure you have never studied computers before No said Pat I have used them but I have never studied how they work They certainly work a lot differently than I would have expected I replied I agree computers work very differently than most people would expect When I first learned about how a computer works I was very surprised and also amazed that humans were capable of developing such a wonderful design In fact Iam still amazed After a few moments I said Lets finish the STA instruction I am going to write your description of how the STA instruction works in the Instruction Table which I did I then asked Pat which memory location should we tell the STA instruction to copy the number in register A to Pat looked at the memory map and said how about putting it into memory location 8 Okay I replied we will place the STA instruction s opcode which is 141 into memory location 4 and place the address that it should write to which is 8 into memory location 5 see Fig 12 Would you like to run this last instruction Pat I said Sure said Pat who then reached out a hand and pressed the run button on the whiteboard The first thing th
99. t what time The cyberspace lock is also capable of having additional information added to it like a user ID so that it can record who is opening it Since cyberspace holds ideas almost any idea you can think of can be placed into this microcontroller as long as the idea is not too big to fit Thats amazing said Pat Computers are becoming more interesting to me all the time I understand a little better now what cyberspace is but it is still kind of fuzzy to me though The only way to gain a better understanding of how cyberspace works I said is to learn how to program computers Learning how to program is very hard work but it is one of the most useful skills a person can have in our modern world The more I learn about computers said Pat the more I want to learn how to program them I am definitely going to take you up on the offer you made earlier to help me For now though I still don t understand what a computer operating system is or how it acts as a bridge between the physical world and cyberspace Operating System The Part Of A Computer Which Is Made From Cyberspace Parts Now that we have discussed both systems in general and cyberspace I said we are in a good position to explain what a computer operating system is We just saw how a normal combination lock can be made more capable and flexible by moving some of its parts into cyberspace There are many systems in the physical wo
100. tches and buttons Programs that are written directly with a CPU s opcodes are called machine language programs Assembly Language The early programmers soon found out however that remembering what all of the opcodes did was difficult and that is when they created mnemonics for each instruction After this they discovered that developing programs using the mnemonics was much easier than using the CPU s opcodes and so programming evolved from using opcodes to using mnemonics After the mnemonic version of a program was developed the programmer would then use documentation similar to our Instruction Table to look up what opcode went with each mnemonic and they would then write these opcodes next to each mnemonic in their program The mnemonic equivalent of the small program we made would look like this Address Opcode Operand Mnemonic amp Operand 000 169 010 LDA 010 002 105 005 ADC 005 004 141 008 STA 008 The Address column holds the beginning address of each opcode the Opcode column holds the opcode and the Operand column contains the data an opcode may need The Mnemonic amp Operand column contains the mnemonic version of the program which the programmer writes first and then fills in the appropriate machine language numbers in the left three columns The number sign next to the numbers 10 and 5 means that these numbers are placed in memory immediately after the instruction s opcode Copyright 2007 by Ted Kosan
101. the book however a surprising thing started to happen I became so interested in what I was reading that I lost track of time and before I knew it an hour had passed During that hour I had learned how to write my first BASIC program and while it was not easy to do there was little pain involved because I was learning this information because I really wanted to It took a month or so to work my way through the User s manual and believe it or not it took me years to master all of the material that was contained in the Reference manual While the information I was learning greatly fascinated me and still does the surprising lesson that I learned was that it was not only possible to learn deep technical information on one s own it was actually a very efficient method for doing so Even later I discovered that self motivated learning is the only kind of learning that is effective As the Teacher said earlier That which is learned without desire is soon forgotten And guess what Today technology is changing the world at such a fast and ever increasing rate that the only way to keep up with this constant change is to be a continuous self motivated learner The following quote from Computer Scientist and futurist Ray Kurzweil supports this statement An analysis of the history of technology shows that technological change is exponential contrary to the common sense intuitive linear view So we won t experience 100 years of pr
102. the keyboard a number between 0 and 255 that represents that key is sent through the cable This number then appears as if by magic in the I O location that the cable is attached to After the number appears in the I O location the CPU can access this same I O location from its left facing opening in order to determine which key had been pressed Thats cool shouted Pat I never would have guessed that a keyboard worked that way but it makes sense I agree I said it does make sense and when I first learned how I O memory locations worked I was as excited as you are The last thing I am going to do with the model of the keyboard is to place an arrow at the end of the cable that is attached to the I O location to show that the keyboard send data into the computer which I did Copyright 2007 by Ted Kosan 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 Version 1 21 Computer Systems 26 77 The next device Iam going to draw is a printer Underneath the printer I drew another horizontal rectangle and wrote the word Printer in it I then drew a line between the printer and another one of the I O memory locations see Fig 17 This is a simplified model of how a printer attaches to a computer Now that you know how a keyboard sends a letter like a capital A to a computer see if you can explain how a capital letter A might be printed on a pr
103. this instruction assume that the first number to be added is already in register A and the second number can be placed immediately after the address of the addition instruction in memory just like with the load instruction Pat pointed to memory location 3 and said Place the number 5 into memory location 3 right after the 105 that represents the addition instruction I said I like that idea and I wrote a 5 in memory location 3 After the addition instruction adds the 10 and the 5 together where should it place the answer Hmmm said Pat that is a good question I am not sure where the answer should go What we could do is to place the answer back into register A since we do not need the number that is there any more What do you think That sounds okay replied Pat The operation description that is placed next to the 105 in the Instruction Table can say something like Adds the number that is in register A with the number in the memory location immediately following the instruction s memory location The answer is placed into register A Very good I said and I wrote this operation description next to the number 105 in the Instruction Table By the way another name for a register that is able to have numbers added with it is an accumulator so we can refer to register A as accumulator A if we would like Also the numbers like 169 and 105 that represent CPU instructions or operations are
104. to control devices that are either on or off Why is that asked Pat T will make a deal with you Pat I said Do some research about computers on the Internet when you go home The next time you come over if you can Copyright 2007 by Ted Kosan 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 Version 1 21 Computer Systems 65 77 tell me why computers love things that are either on or off I will give youa solenoid Is it a deal Its a deal said Pat But are you saying that we are going to puta computer inside of a lock Sure why not I said Microcontrollers Computers On A Chip Isn t a computer too big to fit into a lock Pat replied Some computers are too big to fit into a lock I said but some computers are very small Have you ever heard of a microcontroller No said Pat what is a microcontroller A microcontroller is a complete computer on a chip Inside the chip is the same model of a computer that we have been developing on the whiteboard It has a CPU RAM ROM and I O in it I then went to one of my drawers and returned with a small microcontroller Open your hand Pat I said I then lightly touched Pa s hand with my pinky finger to egualize our charges and then placed the microcontroller in it P
105. ts that the device send the numbers that represent the operating system s machine language instructions to the I O location that the device is attached to one number at a time As each number arrives in the storage device s I O location the CPU copies this number to a register and then it copies the number from the register to RAM An operating system consists of thousands and thousands of machine language instructions so I can not show them all being placed in RAM individually Instead Iam going to draw a vertical bar from the bottom of the RAM upwards which represents RAM being filled with the numbers that represent the operating system which I did see Fig 19 Copyright 2007 by Ted Kosan 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 Version 1 21 Computer Systems 59 77 Figure 19 Memory Map Inside Outside Computer Computer ROM XXX 4 Keyboard XXX b gt Printer pu CPU O1 XXX a Hard Drive Operating System loaded into memory Operating Systems Bridges To Cyberspace What exactly is a computer operating system Pat asked I have always been confused by this I thought about Pat s question for a few moments then said Do you remember earlier when I said that in a way computers were magic because part of a computer exists in the physical world and the other part exists in a non physical realm called cyberspace T remember said
106. uld be difficult to explain without first understanding how a computer works Will you teach me how a computer works asked Pat I really want to know I looked at Pat for a long while before I replied I can teach you a bit about computers Pat but this explanation would only be a beginning and you will need to continue studying computers on your own if you want to really understand them A teacher is mainly a guide and not a substitute for taking responsibility for you own learning I can open some doors for you but it will be up to you to walk through those doors to find out where they lead As long as you understand this I am willing to spend some time explaining how a computer works to you Do you understand T understand said Pat Pull up a chair then I said while I fetch some small whiteboards and a marker When I returned I placed a whiteboard on the table and carefully drew a tall vertical rectangle towards the center of the board As I drew I slowly whistled three progressively higher notes followed by two quicker and even higher notes followed by a low BOM bom BOM bom BOM bom BOM bom I noticed Pat looking at me sideways under raised eyebrows Have you ever seen a movie called 2001 a Space Odyssey I said No Well many people consider it to be one of the best science fiction movies ever made and in the movie scientists find a tall black monolith that had Copyright 2007 by Ted Kos
107. ured out ways to use the low level languages they could already program in to create the high level languages that they wanted to program in This is when languages like FORTRAN in 1957 ALGOL in 1958 LISP in 1959 COBOL in 1960 BASIC in 1964 and C 1972 were created Ultimately a CPU is only capable of understanding machine language and just like assembly language needs to be converted to machine language before a CPU can understand it so it is with all computer languages Compilers And Interpreters How is a high level language converted into machine language asked Pat There are two types of programs that are commonly used to convert a higher level language into machine language I replied The first kind of program is called a compiler and it takes a high level language s source code as its input usually in typed form and converts it into machine language After the machine language equivalent of the source code has been generated it can be loaded into a computer s memory and run The compiled version of a program can also be saved on a storage device and loaded into a computer s memory whenever it is needed The second type of program that is commonly used to convert a high level language into machine language is called an interpreter Instead of converting source code into machine language like a compiler does an Copyright 2007 by Ted Kosan 1200 1201 1202 1203 1204 120
108. volcano Their metabolisms have been increased so much in fact that the atoms in their bodies are vibrating too quickly for the landing party to see This faster vibration results in the Scalosians living in a faster time frame than the crew of the enterprise are At this point I am going to deviate from the story line of this episode in order to better explain the part that is missing from our models of a computer Lets assume that a red shirted crew member screamed and captain Kirk started running across the landscape to investigate Imagine him taking two steps then freezing like a statue in a running position and the other members of the landing party also become frozen At the same time people suddenly appear and they seem to be acting normally They are walking around the frozen landing party members and discussing what they should do about them What has happened is that the perspective has been switched to the faster time frame and we are seeing the world as the Scalosians see it One Scalosian looks at captain Kirk and says we can not let him reach his fallen crew member Let us build a brick wall to stop him and the other Scalosian agrees Have you ever seen a brick wall built Pat No answered Pat Brick walls can not be built by magic I said they must be built using very specific techniques Lets assume that the Scalosians are going to build a Copyright 2007 by Ted Kosan Version 1 21 Computer Systems 75 77
109. w moments and then walked back in and said Give me five in a very calm voice Give you 5 what asked Pat with a look of confusion Can you think of some things I could mean by that statement I said Well said Pat after a few moments if we were in the store buying candy and you had just asked the clerk behind the counter for some chocolate bars the clerk might ask you how many do you want and you could say Copyright 2007 by Ted Kosan 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 694 695 696 697 698 699 700 701 702 Version 1 21 Computer Systems 24 77 Give me five That is a good example I said can you think of another Hmmmm said Pat you could be asking a friend to loan you some money and when the friend asks you how many dollars you need you could say Give me five Good I said now give me one more Pat thought for a while smiled stuck out a hand palm up and said Give me five I smiled in return and slapped the upturned hand Okay Pat I said in each of those three examples the same phrase Give me 5 was used How did the people in each example know what was meant when the phrase was said Pat pondered this question then responded the meaning of Give me five depended on what the people were doing In the first example some candy bars were b
110. what do you think happens Pat thought about this then replied The key is turned into electronic signals and sent to the computer through the keyboard s cable This is true I said but the interesting part is what the electronic signals represent When a key is pressed on a keyboard say the A key the idea of the capital letter A is turned into a number and the electronic signals that are sent through the keyboard s cable represent this number But where does the other end of a keyboard s wire attach to the computer at This is where the I O memory locations come in I O memory locations are special memory locations because not only do they have an opening that faces towards the CPU they also have another opening that faces the outside of the computer The way that a device that is outside the core of a computer sends information into the computer is through one of these I O Copyright 2007 by Ted Kosan 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 Version 1 21 Computer Systems 55 77 memory locations I then drew a line from the left side of the keyboard through the vertical dashed line and into the right side opening of one of the I O memory locations see Fig 16 Figure 16 Memory Map Inside Outside Computer Computer lt a pe ROM Iu CPU a o a XXX XXX RAM This line represents the keyboard s cable and when a key is pressed on
111. y Ted Kosan Version 1 21 Computer Systems 47 77 silly as you trying to walk through your bed Once a garbage instruction has been executed the CPU usually looses track of where it was suppose to be in the program and it continues to execute garbage instructions in memory until somebody pushes the reset button Do you see now how easy it can be to lock up a computer Pat Yes said Pat In fact I was thinking that it seems so easy to lock up a computer that it is a wonder that they do not lock up more often than they do I agree I said and if your PC locks up you just need to restart it If the engine computer on something like a passenger jet locks up however that could be a big problem Wow said Pat I wouldn t want to be on a passenger jet if that happened Pat looked at the ceiling thought for a few moments then said I hear about PC s locking up all the time but I have never heard about the engine computer on a passenger jet or even a car locking up How come one kind of computer locks up a lot but other kinds don t lock up very much at all That is a difficult question to answer completely at this point in our discussion I replied If you ever take me up on my offer to help you to learn how to program a computer though ask this question again and I will try to explain it to you Okay said Pat Now I have a question for you I said If all the RAM memory l

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