Copyright: HAC Simple (c) 1991-1995 by Chet Langin


Simple Table of Contents

The World's Simplest Computer

Table of Contents

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Page 1: 	The World's Simplest Computer
Page 2: 	A Bit Is Like a Bulb
Page 3: 	Bits Can Be Many Things
Page 4: 	Eight Bits Make a Byte
Page 5: 	Half of a Byte Is a Nibble
Page 6: 	A Word Is One or More Bytes
Page 7: 	Review
Page 8: 	Bytes Are Like Characters
Page 9: 	Bytes Are Also Numbers
Page 10: 	One Byte, Two Meanings
Page 11: 	A Primitive Computer
Page 12: 	A Five-Million-Bit Computer
Page 13: 	256 Variations of Byte
Page 14: 	A Byte Can Be Many Things
Page 15: 	ASCII ("As-Key") to the Rescue!
Page 16: 	Is it ASCII?
Page 17: 	(ASCII Illustration)
Page 18: 	Pixels, Light Bulbs, and Bits
Page 19: 	Pixels Copy Bits
Page 20: 	From Characters to Pixels
Page 21: 	Bytes Have Addresses
Page 22: 	The Byte Post Office
Page 23: 	The CPU Is the Handling Area
Page 24: 	Byte Addition
Page 25: 	Adding Bytes from Memory
Page 26: 	Variables Are Assigned Addresses
Page 27: 	Bytes Take the Bus
Page 28: 	The Real Bus
Page 29: 	Memory Maps
Page 30: 	Interrupts Are Traffic Controllers
Page 31: 	RAM Has Many Uses
Page 32: 	In the Chips
Page 33: 	The CPU Chip
Page 34: 	Putting it all Together
Page 35: 	Disk Drives
Page 36: 	The Keyboard
Page 37: 	The Video Display
Page 38: 	Other Add-ons
Page 39: 	Circuit Boards, Part 1
Page 40: 	Circuit Boards, Part 2
Page 41: 	Beware the DIP Switches
Page 42: 	Bugs
Page 43: 	Everything Taken Apart
Page 44: 	Like Many, Like None
Page 45: 	Shrinking the System
Page 46: 	What Is Going on in There?
Page 47: 	The CPU Governs Everything
Page 48: 	Loading the Program
Page 49: 	Following the Program Code
Page 50: 	Typing the Document
Page 51: 	Printing the Document
Page 52: 	Saving the Document
Page 53: 	Other Types of Programs
Page 54: 	Load, Load, Change, Save
Page 55: 	Test
Page 56: 	Answer:  Yes
Page 57: 	It Takes a Program to Write a Program
Page 58: 	Loading the Language
Page 59: 	Typing the New Program
Page 60: 	Translating to Program Code
Page 61: 	Back to Bytes
Page 62: 	The Lowly Bit
Page 63: 	Are Computers Intelligent?
Page 64: 	The World's Simplest Computer (Revisited)


The World's Simplest Computer
Page 1

The World's Simplest Computer

The world's simplest digital electronic computer can handle one piece of information.

It has a keyboard with one switch, and it determines if that switch is on or off.  If the switch is on, it sends electrical energy to the video display to shine a light.  If the switch is off, then it cuts off this energy leaving darkness.

Other digital computers work the same way.  They just combine switches in sophisticated ways.


A Bit Is Like a Bulb
Page 2

A Bit Is Like a Bulb

A bit is one piece of information and is the smallest unit of data which a computer can hold.  Millions of bits can fit on a single computer chip.  The actual physical qualities of a bit inside a computer can vary, but a bit can be, for example, a surge of electrical energy or a magnetic field.

Imagine that a lit light bulb represents a bit which is on.  An unlit light bulb represents a bit which is off.  Imagine that the computer can detect whether the bit is on or off.

This bit is off:  	This bit is on:


Bits Can Be Many Things
Page 3

Bits Can Be Many Things...

  /  	   /  	       /  	 /
Off/On 	No/Yes 	False/True 	 0/1

      /  	          /  	      /  	       /
Male/Female 	Pepper/Salt 	Night/Day 	None/One

Someone who does not know about bits/Someone who is learning about bits

...It Is Up to the Programmer!


Eight Bits Make a Byte
Page 4

Eight Bits Make a Byte

Other sized bytes are possible, but this is the generally accepted size for IBM compatible personal computers.  It is easy to remember the difference between bits and bytes.  The word byte is longer than the word bit and bytes are longer than bits.

Byte is pronounced bite.  It is spelled with the character y instead of the character i to help distinguish the word byte from the word bit.

A lot of word plays are done on byte.  Prepare a groan for the next page.


Half of a Byte Is a Nibble
Page 5

Half of a Byte Is a Nibble

Really!

Nibble is sometimes spelled nybble to be consistent with the spelling of byte.

Programmers like nibbles because they make it easier to translate from the binary numerical system to the hexidecimal numerical system.  You may not want to know the details about why this is true, but it is fun to know that half a byte is a nibble!


A Word Is One or More Bytes
Page 6

A Word Is One or More Bytes

The size of a word is set by the manufacturer of a computer and represents how many bits a computer can process at the same time.

The current trend towards 32-bit computing means that 32 bits, or four bytes, is the word size.

The above illustration shows a 16-bit, or two-byte, word.


Review
Page 7

Review

A bit:
A nibble:
A byte:

A Word:


Bytes Are Like Characters
Page 8

Bytes Are Like Characters

Characters make up real words and bytes make up computer words.  However, there is another way that bytes are like characters.  A computer stores characters in bytes.  The combination of on bits in a byte signifies to the computer which character it represents.

Note:  There is a current movement, called Unicode, towards having two bytes per character instead of one byte.


Bytes Are Also Numbers
Page 9

Bytes Are Also Numbers

Bytes can represent numbers as well as characters.

When a byte is a number, the combination of lit bits signifies to the computer what number it represents.

How does a computer know if a bit is a number or a character?  The programmer tells it through programming code.


One Byte, Two Meanings
Page 10

One Byte, Two Meanings

The programmer instructs a computer to interpret particular bytes as numbers or as characters.  These computer code instructions are also represented as bytes.  So bytes can represent numbers, characters, or computer code.  They can also represent other things.

 When a computer starts, it looks at a particular byte and interprets it as computer code for what to do next.  Programmers take over from there to instruct the computer on how to interpret other bytes.


A Primitive Computer
Page 11

A Primitive Computer

This is an imaginary and oversimplified concept of a primitive computer.  However, early personal computers were similar to this.  For example, they had switches to set individual bits.  After the computing was finished, the user had to read and interpret lights which also represented individual bits.

These early computers did not have keyboards, video displays, printers, or disk drives.


A Five-Million-Bit Computer
Page 12

A Five-Million-Bit Computer

 Most personal computers have at least 640k of Random Access Memory (RAM).  Since a single k is 1,024, this means that these computers have (640 times 1,024 equals) 655,360 bytes of RAM.  Since each byte has eight bits, this means that these computers have (8 times 655,360 equals) 5,242,880 bits in RAM.

While the light bulbs have been convenient, so far, in representing bits, they would become clumsy as this discussion of bits and bytes progresses.  Therefore, a new method is going to be used:  That of using 0's and 1's.  A 0 represents a bit (light) which is off, and a 1 represents a bit (light) which is on.

The byte in the illustration can now be stated simply as being 01100101 without the use of any graphical pictures of lights.


256 Variations of Byte
Page 13

256 Variations of Byte

The bits in a byte can be arranged 256 ways.  Scroll down the illustration and you may be able to detect and abstract pattern of how the bit counting progresses.  (If you can't, don't fret.  Just recognize that their are 256 possibilities.)

00000000 = 0
00000001 = 1
00000010 = 2
00000011 = 3
00000100 = 4
00000101 = 5
00000110 = 6
00000111 = 7
00001000 = 8
00001001 = 9
00001010 = 10
00001011 = 11
00001100 = 12
00001101 = 13
00001110 = 14
00001111 = 15
00010000 = 16
00010001 = 17
00010010 = 18
00010011 = 19
00010100 = 20
00010101 = 21
00010110 = 22
00010111 = 23
00011000 = 24
00011001 = 25
00011010 = 26
00011011 = 27
00011100 = 28
00011101 = 29
00011110 = 30
00011111 = 31
00100000 = 32
00100001 = 33
00100010 = 34
00100011 = 35
00100100 = 36
00100101 = 37
00100110 = 38
00100111 = 39
00101000 = 40
00101001 = 41
00101010 = 42
00101011 = 43
00101100 = 44
00101101 = 45
00101110 = 46
00101111 = 47
00110000 = 48
00110001 = 49
00110010 = 50
00110011 = 51
00110100 = 52
00110101 = 53
00110110 = 54
00110111 = 55
00111000 = 56
00111001 = 57
00111010 = 58
00111011 = 59
00111100 = 60
00111101 = 61
00111110 = 62
00111111 = 63
01000000 = 64
01000001 = 65
01000010 = 66
01000011 = 67
01000100 = 68
01000101 = 69
01000110 = 70
01000111 = 71
01001000 = 72
01001001 = 73
01001010 = 74
01001011 = 75
01001100 = 76
01001101 = 77
01001110 = 78
01001111 = 79
01010000 = 80
01010001 = 81
01010010 = 82
01010011 = 83
01010100 = 84
01010101 = 85
01010110 = 86
01010111 = 87
01011000 = 88
01011001 = 89
01011010 = 90
01011011 = 91
01011100 = 92
01011101 = 93
01011110 = 94
01011111 = 95
01100000 = 96
01100001 = 97
01100010 = 98
01100011 = 99
01100100 = 100
01100101 = 101
01100110 = 102
01100111 = 103
01101000 = 104
01101001 = 105
01101010 = 106
01101011 = 107
01101100 = 108
01101101 = 109
01101110 = 100
01101111 = 111
01110000 = 112
01110001 = 113
01110010 = 114
01110011 = 115
01110100 = 116
01110101 = 117
01110110 = 118
01110111 = 119
01111000 = 120
01111001 = 121
01111010 = 122
01111011 = 123
01111100 = 124
01111101 = 125
01111110 = 126
01111111 = 127
10000000 = 128
10000001 = 129
10000010 = 130
10000011 = 131
10000100 = 132
10000101 = 133
10000110 = 134
10000111 = 135
10001000 = 136
10001001 = 137
10001010 = 138
10001011 = 139
10001100 = 140
10001101 = 141
10001110 = 142
10001111 = 143
10010000 = 144
10010001 = 145
10010010 = 146
10010011 = 147
10010100 = 148
10010101 = 149
10010110 = 150
10010111 = 151
10011000 = 152
10011001 = 153
10011010 = 154
10011011 = 155
10011100 = 156
10011101 = 157
10011110 = 158
10011111 = 159
10100000 = 160
10100001 = 161
10100010 = 162
10100011 = 163
10100100 = 164
10100101 = 165
10100110 = 166
10100111 = 167
10101000 = 168
10101001 = 169
10101010 = 170
10101011 = 171
10101100 = 172
10101101 = 173
10101110 = 174
10101111 = 175
10110000 = 176
10110001 = 177
10110010 = 178
10110011 = 179
10110100 = 180
10110101 = 181
10110110 = 182
10110111 = 183
10111000 = 184
10111001 = 185
10111010 = 186
10111011 = 187
10111100 = 188
10111101 = 189
10111110 = 190
10111111 = 191
11000000 = 192
11000001 = 193
11000010 = 194
11000011 = 195
11000100 = 196
11000101 = 197
11000110 = 198
11000111 = 199
11001000 = 200
11001001 = 201
11001010 = 202
11001011 = 203
11001100 = 204
11001101 = 205
11001110 = 206
11001111 = 207
11010000 = 208
11010001 = 209
11010010 = 210
11010011 = 211
11010100 = 212
11010101 = 213
11010110 = 214
11010111 = 215
11011000 = 216
11011001 = 217
11011010 = 218
11011011 = 219
11011100 = 220
11011101 = 221
11011110 = 222
11011111 = 223
11100000 = 224
11100001 = 225
11100010 = 226
11100011 = 227
11100100 = 228
11100101 = 229
11100110 = 230
11100111 = 231
11101000 = 232
11101001 = 233
11101010 = 234
11101011 = 235
11101100 = 236
11101101 = 237
11101110 = 238
11101111 = 239
11110000 = 240
11110001 = 241
11110010 = 242
11110011 = 243
11110100 = 244
11110101 = 245
11110110 = 246
11110111 = 247
11111000 = 248
11111001 = 249
11111010 = 250
11111011 = 251
11111100 = 252
11111101 = 253
11111110 = 254
11111111 = 255

That's only 255!?

No it isn't.  When you count the first byte, which starts at 0, then it's 256 variations.


A Byte Can Be Many Things
Page 14

A Byte Can Be Many Things

How can anybody tell when a byte stands for what?


ASCII ("As-Key") to the Rescue!
Page 15

ASCII ("As-Key") to the Rescue!

ASCII stands for the American Standard Code for Information Interchange.  It is used so that bytes can be utilized in a consistent manner.

With non-ASCII code, only the programmer knows for sure what the bytes stand for.


Is it ASCII?
Page 16

Is it ASCII?

   One can tell if a file uses the ASCII format by loading it into an ASCII text editor (such as Windows Notepad).  If the file can be read, it is ASCII.  ASCII files are sometimes called text files.  If the file is not ASCII, it produces nonsense, and sometimes beeps.


(ASCII Illustration)
Page 17

The bytes listed below stand for the indicated characters and cause the message in the illustration to be shown on the video display.

01000100 = "D"
01100001 = "a"
01100100 = "d"
00101100 = ","
00001101 = Carriage Return
00001010 = Line Feed
00100000 = (Space)
01010011 = "S"
01100101 = "e"
01101110 = "n"
01100100 = "d"
00001101 = Carriage Return
00001010 = Line Feed
00100000 = (Space)
01101101 = "m"
01101111 = "o"
01101110 = "n"
01100101 = "e"
01111001 = "y"
00011010 = End Of File


Pixels, Light Bulbs, and Bits
Page 18

Pixels, Light Bulbs, and Bits

A pixel is a single dot on a video screen.  Pixel stands for picture element.  A video screen contains many thousands of pixels.  If a pixel is on for a monochrome monitor, it displays a dot on the screen.  Otherwise, it does not.  Pixels have similarities to light bulbs and bits.

This off pixel, [image],
is similar to this light bulb, [image],
which is similar to this bit, 0.

This on pixel, [image],
is similar to this light bulb, [image],
which is similar to this bit, 1.


Pixels Copy Bits
Page 19

Pixels Copy Bits

For monochrome graphical displays, the pixels copy the status of bits located in a certain part of the computer's memory.


From Characters to Pixels
Page 20

From Characters to Pixels

Characters are first changed from their ASCII codes to their graphical bit structures.

The manufacturer of the computer often places these bit structures in the memory of the computer when it is made.

Then, the status of each bit is copied to the corresponding pixel on the video display.

Color displays are done by using more bits, which contol the different colors for each pixel.


Bytes Have Addresses
Page 21

Bytes Have Addresses

Every byte in the computer has its own address

where it can be located immediately.


The Byte Post Office
Page 22

The Byte Post Office

The best way to visualize byte addresses is to think of them as being post office boxes.

This way, they can be referred to by their box numbers.

For example, the byte in Box 6 is 01001001.

Any random byte can be directly accessed this way.  That is why this method is called random access memory (RAM).


The CPU Is the Handling Area
Page 23

The CPU Is the Handling Area

CPU stands for Central Processing Unit.  It is where the computer actually does things with the bytes (besides just storing them).  The CPU also has addresses for its bytes.


Byte Addition
Page 24

Byte Addition

Before proceeding, it is desirable to know something about how to add two bytes.  It is the same as normal arithmetic, except that the highest possible digit is 1.  It is not necessary to understand exactly how to add bytes.  But one should know that a method does exist.


Adding Bytes from Memory
Page 25

Adding Bytes from Memory

Any two bytes can be added from anywhere in RAM and the result placed anywhere in RAM.

Each number is placed in the CPU where the addition takes place.

The answer is placed back in memory.  The programmer decides where the bytes come from and where the answer goes to.


Variables Are Assigned Addresses
Page 26

Variables Are Assigned Addresses

When a program uses a variable, it is assigned an address in RAM.

Whatever byte is in that address, is what the variable stands for.


Bytes Take the Bus
Page 27

Bytes Take the Bus

When a byte in RAM goes to or from the CPU, it takes the bus, which is an internal network of connections which allows different parts of the computer to communicate with each other.


The Real Bus
Page 28

The Real Bus

Actually, the computer bus looks somewhat like a railroad switching yard.  It is located on the motherboard, which is the main circuit board inside the computer cabinet.  Each bit has its own track so that the entire byte can move at once.  The bus on many computers has even more tracks and can move more than one byte at a time.


Memory Maps
Page 29

Memory Maps

In order to keep track of the many, many thousands of addresses of bytes, programmers often use memory maps to remember what type of information is stored where.

For example, a commonly known memory location in many personal computers is B800 in hexadecimal notation.  Translated to the decimal numerical system, it is 47,104.  In byte form, it is 10111000-00000000.

This is the address in these computers where the video display bytes begin.


Interrupts Are Traffic Controllers
Page 30

Interrupts Are Traffic Controllers

As the bytes travel around inside the computer, a way is needed to control which bytes have the right-of-way over others.

Interrupts perform this task.  For example, which should a computer do first:  Show a character on the video display or determine if a key is pressed on the keyboard?

An interrupt decides which to do first.


RAM Has Many Uses
Page 31

RAM Has Many Uses

RAM was illustrated a few pages ago like post office boxes.  Here, it is illustrated a little differently.

While the RAM contains individual bytes, it also has groups of bytes.  For example, one group of bytes contains machine language code to tell the computer what to do.  Another group contains the variables used in a program.  Still another contains the bits which tell how to light up the pixels in the video display.  Some bytes are used to hold other information, and some are not used, at all.

 The CPU keeps track of where these different groups of bytes are located.


In the Chips
Page 32

In the Chips

The RAM is actually located on a bank of computer chips inside the computer cabinet.  The diagram on the left, with the chips, does not demonstrate how the RAM chips are used.  The diagram on the right illustrates that the RAM is used for holding bytes related to machine language code, variables, the video, and other information.


The CPU Chip
Page 33

The CPU Chip

The CPU is located on one large computer chip.  The diagram on the right is to illustrate that the CPU has internal addresses for different bytes which it uses for addition and other chores.  A CPU actually has room for much more than three bytes and has address names besides A, B, and C.


Putting it all Together
Page 34

Putting it all Together

In the next few pages, an illustration of a symbolic computer will be put together.

The bus, introduced on pages 27 and 28, forms the backbone.

Here, the RAM and the CPU are connected to the bus, which comes up out of the RAM on the left, crosses over the top, and goes down into the CPU on the right.


Disk Drives
Page 35

Disk Drives

Bytes are stored magnetically on computer disks.  A disk drive reads the bytes off of the disk and stores them in RAM.  Disk drives can also copy bytes from RAM and store them on a disk.

Although disks are held in square sleeves, they are actually round.  Inside the computer cabinet, the physical disk drive looks like a small box.  It is connected internally by a cable to the bus.


The Keyboard
Page 36

The Keyboard

The keyboard has a cable which attaches to the bus.

When a key is pressed, the byte representing the character for that key is sent to an interrupt, where it waits until the program code looks for it.


The Video Display
Page 37

The Video Display

The video display also attaches to the bus.


Other Add-ons
Page 38

Other Add-ons

Other components of a computer, such as a mouse, joystick, modem, and printer, also attach to the computer through the bus and communicate with it using bytes.


Circuit Boards, Part 1
Page 39

Circuit Boards, Part 1

It will be shown on the next page how circuit boards are used to plug devices into the bus.

But, first, it needs to be shown that the bus will be rotated on the next page as shown here.


Circuit Boards, Part 2
Page 40

Circuit Boards, Part 2

Many computers use circuit boards to attach printers and other devices to the bus.

These circuit boards are sometimes called cards.

The circuit board plugs into the bus inside the computer cabinet.  Then, the cable from the device plugs into the circuit board through a hole in the back of the computer.


Beware the DIP Switches
Page 41

Beware the DIP Switches

DIP stands for Dual In-line Pins.  It means that a chip, or, in this case, a group of switches, have a row of pins on each side that plug into a circuit board.  DIP switches are tiny manual switches that manufacturers install in various parts of a computer.  They often have eight switches which correspond to the eight bits in a byte.

 Here is an overhead view of a DIP switch.  The pins go across the top and bottom and aim downwards.  A row of switches goes across the middle and is set in this pattern:  10011001.

DIP switches are set by humans and are so small that it takes a pointed object, like an ice pick, to change a setting.  They can be almost anywhere, inside the computer cabinet, on the back of a keyboard, or inside a printer.  They control certain aspects of the operation of a computer which rarely need to be changed.  For example, a DIP switch may be set to make a certain keyboard compatible with a certain computer.


Bugs
Page 42

Bugs

The first computer bug was really a bug which got stuck in one of the earliest mainframe computers.

Today, bugs can still be found inside many computers.  Just take the cover off of the cabinett and look near the cobwebs!

But, really, when programmers say "There is a bug in it," they mean that some is wrong with a program.  That it does not work correctly.

When programmers debug their programs, it means that they are looking for and removing all of the errors in it.


Everything Taken Apart
Page 43

Everything Taken Apart


Like Many, Like None
Page 44

Like Many,
Like None

This symbolic computer is like many in the way it shows how the various parts work together.  However, it does not represent any actual computer.


Shrinking the System
Page 45

Shrinking the System

The illustration is being shrunk down to size to make further explanations easier.

Note that the CPU is not to scale even in this smaller illustration.  It is actually on a single chip inside the computer cabinet.

Some things have been left out:  The power supply, the speaker, and the cooling fan, for example.  They do not contribute much towards understanding how a computer works.


What's Going on in There?
Page 46

What's Going on in There?

With so much going on inside the computer, many users do not understand where the data is at in there.

Sometimes their data disappears and they do not know why.

Over the next few pages, the illustrations will show what happens inside the computer during popular types of programs.


The CPU Governs Everything
Page 47

The CPU Governs Everything

The CPU rules all of the other parts of the computer.

It does this by sending codes, in the form of bytes, through the bus to the other components.

The CPU gets feedback in the same way on such matters as the values as variables, the status of the program, and whether the printer is ready.


Loading the Program
Page 48

Loading the Program

A word processing program is used as the first example.

The program, which has been stored on a disk, is sent through the bus and is put into RAM.

The program is stored on the disk in the form of bytes.  It is also sent through the bus and saved in RAM as bytes.


Following the Program Code
Page 49

Following the Program Code

Once the program code is in RAM, it is read by the CPU.

The CPU will obtain an instruction from the program code and then direct the appropriate part of the computer to perform that instruction.

The CPU will then get the next instruction, and the next, going on down the sequence of program code, performing each one in order.


Typing the Document
Page 50

Typing the Document

In the word processing program, as the user types the document, it is placed into variables in RAM.

Following the directions of the program, the document is also transferred from the variables to the part of RAM which designates the video display.

It is actually in two locations in RAM.  First, in the variables location; and, second, in the video display location.  Of course, all of this is in the form of bytes.


Printing the Document
Page 51

Printing the Document

When a copy of the document is printed, it is sent from the variables in RAM to the printer.

This transfer is done through the bus in the form of bytes.

Do not forget that the CPU is directing these activities.  Arrows to and from the CPU have been omitted for the sake of simplicity.


Saving the Document
Page 52

Saving the Document

Once the document is finished, it can be saved to the disk for future use.

It is transferred from the variables in RAM through the bus to the disk drive.  Of course, all of this is done in the form of bytes and is controlled by the CPU.

Even though the document has been put on the disk, it is still also in RAM until it is cleared, or overwritten by other data, or until the computer is turned off.


Other Types of Programs
Page 53

Other Types of Programs

Game:  	Planner:  	Tutor:

 Other types of programs work in a similar way to a word processing program.  First, the program, itself, is loaded from the disk drive into RAM.  Second, if any data is being used from a previous session, it is loaded into RAM from the disk drive.  Third, the data is increased, changed, or decreased by the user.  Finally, the data is transferred from RAM back to the disk drive and onto a disk.

Spreadsheet:  	Database:  	Graphics:


Load, Load, Change, and Save
Page 54

Load, Load, Change, and Save

Most programs are similar in this respect:  You load the program, then load the data, then change the data, and then save the data.

 (1) The program is loaded from the disk into RAM.

(2) Previous data, if any, is loaded from the disk into RAM.

(3) The data is changed from the keyboard.

(4) The new or changed data is saved from RAM to the disk.


Test
Page 55

Test

(1) Load.

(2) Load.

(3) Change.

(4) Save.

A word processing program has been loaded into the computer along with a document for a long-term project.  The user accidentally ruins the document.  Can the document be salvaged?


Answer:  Yes
Page 56

Answer:  Yes

In the test, only the first three steps had been done.  Therefore, the original document is still on the disk.  To salvage it, go back to Step 2 and load it, again, from disk into RAM.

(1) Load.

(2) Load.

(3) Change.

(4) Save.


It Takes a Program to Write a Program
Page 57

It Takes a Program to Write a Program

A programming language is needed in order to program a computer, and a programming language is a program, itself.

Many new computer users try the BASIC programming language.  This stands for Beginner's All-purpose Symbolic Instruction Code.

Many other types of programming languages are available, such as C, Pascal, Fortran, Cobol, and others.

Sometimes a computer is distributed with a programming language, such as BASIC, included.  More often, a programming language has to be purchased separately.


Loading the Language
Page 58

Loading the Language

In order to begin programming, the language must first be loaded into RAM.

It is probably loaded from a disk.  However, with BASIC, it is possible that it may be loaded from a read-only memory (ROM) chip.


Typing the New Program
Page 59

Typing the New Program

As the program is typed, in BASIC or whatever other programming language is being used, it is saved as ASCII text in variables in RAM.

The newly written program can be saved to a disk in this text format, to be recalled and worked on, again, later.


Translating to Program Code
Page 60

Translating to Program Code

Before the newly written program can be performed by the computer, it has to be translated to machine language.

This translation is done internally by the CPU, using RAM and following the directions of the programming language.

Once the newly written program has been changed to machine language, most programming languages allow it to be saved to a disk as a program.


Back to Bytes
Page 61

Back to Bytes


The Lowly Bit
Page 62

The Lowly Bit

A bit is nothing but 1/8 of a byte.  It is the smallest unit of information which a computer can handle.

A bit is similar to a light bulb in that it can be either on or off.

However, everything that a computer does, it does with bytes.  Since bytes are made of bits, this means that all that a computer can do is done with little pieces of information that can be either on or off.  Bits!


Are Computers Intelligent?
Page 63

Are Computers Intelligent?

Humans have developed a revolutionary machine where millions of tiny switches can represent numbers, characters, and, even, complex ideas.  The switches, themselves, are no smarter than light bulbs which can be turned on and off.  But, humans have devised ways to combine these switches to represent ideas.

It is not the switches which are intelligent.

It is the humans.


The World's Simplest Computer (Revisited)
Page 64

The World's Simplest Computer (Revisited)

Just as humans use switches to turn room lights on and off, they can use millions of switches in computers to represent complex ideas.

Reduced to its simplest form, all a computer is...

...is a switch.


HAC Simple
HAC 1.04

HAC Simple

Required skill:  Ability to use Windows Help System, which this uses.  Suggestion:  Select one of the books below.


HAC Timer

You have 30 days to try out this Shareware product.  After that, you are required to register it.

This notice does not appear on registered versions.

Press a key or mouse button to continue.


Before

Before:

HAC Simple is copyrighted, 1991-1995, by Chet Langin, Langin Software, 532 W. 3rd Street, Centralia, IL 62801-5407, USA.

All rights reserved.  No warranty is expressed or implied.

HAC stands for HyperActive Components.

It is Hyper because it uses hypertext.

It is Active because it includes the latest information which is popularly available.

It is Components because it can be integrated with other software.

Go to During.


After

After:

If you continue to use HAC Simple after 30 days, or if you use it for training purposes, then you are required to register it.  The registered version does not have the registration reminder screen at the beginning, and it will contain corrections and refinements, if needed.

You can also order other components.  For descriptions, see HAC Help During.

To obtain the latest version of HAC Simple, send $9.95 plus $4.00 shipping and handling to...

Langin Software

532 W. 3rd St.

Centralia, IL  62801-5407  USA

Or select Order Form to order a component.


Order Form

Print order form.

HAC Simple Order Form

Your Name: 	_______________________________________

Address: 	_______________________________________

Address: 	_______________________________________

City, State, Zip: 	_______________________________________

Ordering Fees:

Item	Price	Number	Extension
HAC DOS*	$9.95	________	________
HAC Glossary*	$9.95	________	________
HAC Simple*	$9.95	________	________
Shipping/Handling			$4.00
Total Amount Due			________

*Notes:  HAC Help is sent free with the order of any other
 component.  Orders are sent on 3.5-inch, high-density disks.

Send to:

Langin Software
532 W. 3rd St.
Centralia, IL  62801-5407 USA


What's New

What's New:

The World's Simplest Computer was originally released as a collection of GIF (graphic interchange format) files.  It was then redesigned to fit the Windows Help format and was included in a huge product called SunShine, which turned out to be impractical because of its large size.  The World's Simplest Computer has been compiled again in the HAC format (and nicknamed HAC Simple) so that with the reduced size it can be distributed on its own, or as a part of the larger overall HAC system.