Index

Numbers

0 (zero) and 1 (one)

Boolean algebra, 45

AND gates and, 7475

importance of, 9495

as “no” and “yes,” 47, 117118

8-bit adder, 180182, 202, 205, 210, 227, 303

6800 microprocessor, 313, 421, 428

8080 microprocessor. see Intel 8080

A

accumulating adders, 227228, 231232, 290, 293

accumulators, 335341, 343, 345346, 383

adding machines

8-bit edge-triggered, 289290

ALU as, 319323

automated, 289314

logic gate based, 169182

relay computers as, 183184

subtraction with, 202206, 210

addition tables, 97, 104, 111

address bus, 346, 348

Aiken, Howard, 184, 430

algebra, 4244

ALGOL, 431

algorithms, 94, 439

al-Khwarizmi, Muhammed ibn Musa, 94

Allen, Paul, 432, 433

Altair 8800, 288, 312, 318

Alto, 420421

ALU (arithmetic logic unit)

accumulator in, 335336

bitwise AND operations, 327

byte movement in, 335

flags, 333

function bits, 328

function of, 319, 320, 355

inputs, 332, 357358

Ampère, André-Marie, 27

amperes/amps, 27, 28

amplifying signals, 62, 68, 88, 189

analog, 184, 408

Analytical Engine, 185, 186

AND (class intersection), 47, 48, 51, 54, 66

AND gates

3-input, 75, 89, 115

clock building with, 255256

flip-flop, 222, 223, 224, 238, 248, 268

memory assembly, 268, 271, 272, 275, 277, 278

output/input, 87, 172

silicon chip, 195

subtraction with, 210

symbol for, 7475

transistor-based, 191

AND operators, 90, 326, 392

Android, 423

anodes, 24

ANSI character set, 160, 161, 441

API (application programming interface), 418, 422

Apple, 421, 422, 423

Apple DOS, 422

Apple II, 419, 420

apps, 418

area codes, 122

arguments, 397

Aristotle, 41, 46

Arithmetic Language, 430

ASCII (American Standard Code for Information Interchange)

ALU use, 323324, 326

characters, 153158

converting numbers to, 414415

extensions, 160162

keyboards codes and, 406407

memory and, 159

ASL (American Sign Language), 3

ASM program, 426427

assembly language, 425430

associative indexing, 449

associative rules, 43, 44, 46

AT&T, 423, 452

Atanasoff, John V., 188

Atkins, Kathleen, viiiix

atoms, 23

Automated Accumulating Adder, 295, 297, 298, 303, 304

AWG (American Wire Gauge), 49

B

Babbage, Charles, 111, 184186

Barbier, Charles, 14

barcodes, product, 126131

Bardeen, John, 189

base-two logarithm, 123

base-ten system, 92, 97, 99

BASIC, 431432

batteries, 2426, 33

Baudot codes, 150153

BCD (binary-coded decimal), 242243, 252253, 331

BDOS (Basic Disk Operating System), 418

Bell 103, 452

Bell Labs, 183, 189, 423

Berners-Lee, Tim, 454

big-endian method, 163, 164, 300, 313

binary codes

Braille, 15, 19, 150

electrical circuits and, 29

Morse code, 6, 12, 149150

powers of two in, 103

shift and escape codes in, 19

telegraph’s use of, 61

binary numbering

adding machines for, 169182

adding/multiplying, 111112, 391

bits as digits in, 116, 118

counting in, 236

decimal equivalents, 112113, 441

digital revolution via, 111

electricity and, 114

hexadecimals and, 142, 143

octal equivalents, 113114

possibilities conveyed by, 120123

subtraction and, 200202

system described, 106109

two’s complement, 208

BIOS (Basic Input/Output System), 417, 418

bitmaps, 408

bits

building blocks as, 118

coining of term, 116

hidden messages in, 123126

memory and, 285

multiples of, 139

possibilities conveyed by, 121123

QR code, 132, 134138

sum and carry, 170171

UPC barcodes, 126131

bitwise AND operation, 327, 392

bitwise OR operation, 325

blocks, 431

BOM (byte order mark), 164

Boole, George, 42, 44, 49, 56

Boolean algebra, 4256, 90, 323, 439

Boolean tests, 4756

bootstrap loader, 417

borrowing, in subtraction, 197199

Braille

code description, 1419

communication via, 3, 150

eight-dot, 19

Grade 2, 1719

invention of, 1314

Braille, Louis, 13, 16, 17

Brattain, Walter, 189

Burks, Arthur W., 188

Bush, Vannevar, 184, 448450, 451, 457

busses, 346, 348, 355, 356

buzzers, 213215

Byron, Augusta Ada, 186, 379, 432

bytes

ASCII characters and, 159

assembling memory, 269

hexadecimal system and, 140141, 143

movement within the CPU, 335339, 342

C

C programming language, 432433

CALL instruction, 395402, 426, 427

cameras, digital, 408409

Campbell’s products, 127, 129, 130

Carriage Return code, 157158

carry bits, 170172, 175, 177, 179, 196

cascading, 182

cathodes, 24

CDs (compact discs), 410

cells, memory, 276

characters

Braille, 16, 1719

EBCDIC, 158

encoding, 149

graphic and control, 155156

Morse code, 26, 711

non-Latin coding, 160, 162

charge, electrical, 2324

chips, 192196, 312

circuits, electrical

batteries in, 26

binary counters, 236

binary numbers and, 29, 114

commons in, 3335

De Morgan’s laws for, 90

description of, 2224, 2629

grounds/earths in, 3538

hardware as, 311

increment/decrement, 350

logic exercises via, 53

memory within, 219220

networks, 6566

non-circular, 38

oscillator, 213216

seven register CPU, 344346

tri-state buffers, 280281

writing relay, 6788

classes, algebraic, 4345, 47

Clear inputs, 238, 244, 298

clients, 453

clock building, 241266

Clock input, 216, 223, 228231, 295297

cloud, the, 457

CMOS chips, 193

COBOL, 431

code cathode displays, 251

code page identifiers, 162

Code: The Hidden Language of Computer Hardware and Software (Petzold), viiix

CodeHiddenLanguage.com, viii, 132, 454, 455, 456

codes

ASCII, 153158

Baudot codes, 150153

binary. see binary codes

Braille, 1419

coding and, 425445

communication via, 13

errors in, 17

keyboard, 406407

language as, 91

Morse code, 26, 712

precedence/shift, 19

Quick Response (QR) code, 131138

UBC barcodes, 126131

used by computers, 34

see also instruction codes; operation codes

coding, 425445

coin flips, 12

color, pixel, 144, 404

command processor, 415416

comments, 390

commons, in circuits, 3335

communication

around corners, 3133, 38

bits for, 123126

development of, 12, 3

long-distance digital, 451452

noise and, 120

telegraph, 5860

commutative rules, 43, 44

Compare operation, 331

compilers, 429, 430, 432

Complex Number Computer, 183

compression, 408409, 411

computers

adding machines as, 169

chips, 192196

components of, 315

decimal-based, 111

history of, 183189

language of, 34

microprocessors in, 312313

transistors in, 189192

use of electricity in, 21

conditional jump, 382, 386, 387

conductors, electrical, 26, 3335, 189

control panels

binary adding machine, 171, 178, 203

RAM, 285287, 291

software installs via, 414

wiring, 6788

control signals, 295, 355378

conventional algebra, 42, 4344, 4546

counters, 192, 236237, 382

counting

binary number, 236

decade counters, 245

decimal, 92

early systems of, 93

flip-flops for, 220, 294

CP/M (Control Program for Microcomputers), 417419, 422, 426

CPU (central processing unit)

components, 319, 356359

control signals, 355378

function of, viiviii, 316, 402

machine cycles, 360362

movement of bytes in, 335348

program for, 317319

speed of, 316

current, 27, 28, 264

cycles, 360362, 379

cycles, oscillator, 216, 217

D

daguerreotypes, 57

data

bytes following codes as, 339

communication long-distance, 451452

level-triggered flip-flop, 220225

memory as code and, 315, 319

data bus, 346, 355

Data In, 221231, 235, 238, 268274, 287

Data Out, 272287, 292, 293, 297, 298

data type indicators, 136

DBCS (double-byte character sets), 162

De Morgan, Augustus, 90, 186

De Morgan’s laws, 90

debugging, 433, 440

decade counters, 245

decimal system

BCD (binary-coded decimal), 242243

binary conversions, 109113, 441

computers based on, 111

counting in, 92

counting in the, 97

hexadecimals and, 142, 143, 145148

multiplication in, 391

naturalness of, 99

octal conversions, 102104

subtraction and, 199, 200201, 206210

decoders/decoding

2-to-4, 305, 306307

3-to-5, 264, 265

3-to-8, 115, 271, 272, 344

4-to-16, 276279, 282

BCD, 252256, 266

errors, 17

Unicode, 165167

decrements, 350, 355, 369, 390

Difference Engine, 185

Differential Analyzer, 184

digitization

analog/digital conversion, 408

clock, 241266

data, as bytes, 140

sound, 409411

diodes, 258, 261

disks, storage, 411412, 418

display, clock, 251266

display, video, 403406, 408, 420421

distributive rules, 43, 44

Dodgson, Charles, 41

dollar/number conversion, 298302

dot matrix, 257258

DRAM (dynamic RAM), 285

Dummer, Geoffrey, 192

E

earth, grounding via, 3538

EBCDIC (Extended BCD Interchange Code), 158159

Ebert, Robert, 121122

Eccles, William Henry, 219

edge-triggered flip-flop, 228239, 243, 289290

Edison, Thomas, 21, 410

EDVAC (Electronic Discrete Variable Automatic Computer), 188

electrical circuits. see circuits, electrical

electricity, 2129, 114, 213215

electromagnetism, 5859, 6870, 214

electromechanical computers, 184

electromotive force, 28

electrons, 2326, 37

emojis, 164

Enable signal, 280, 281, 304

encapsulation, 176

encoders/encoding, 17, 115, 149

Engelbart, Douglas, 421

ENIAC (Electronic Numerical Integrator and Computer), 188

Eratosthenes, 439

errors, 17, 163, 386

escape codes, 19

exabytes, 285

Exclusive OR gate, 175176

executable files, 427, 430

execution, instruction, 361, 363, 364, 372376

F

fan outs, 88

feedback, 218

Festa, Scout, ix

Feynman, Richard, 440

fiber-optic cables, 453

filenames, 157, 417

files, 416417, 427

flags, 331, 333

flashlights, 16, 2129

Fleming, John Ambrose, 187

flip-flops

building, 217240

clock made of, 243249

memory storage via, 267273

floating-point numbers, 441445

Forest, Lee de, 187

Formal Logic (De Morgan), 90

FORTRAN, 430431

fractions, 96, 211, 441444

frequency, oscillator, 217, 235, 237

frequency dividers, 235, 296

Fuchs, Jim, ix

full adders, 177, 179180

function tables, 220223, 225, 230, 232

G

Gates, Bill, 432, 433

GIF (Graphics Interchange Format), 409

gigabytes, 284

GNU, 424

Goldstine, Herman H., 188

Google Books, 457, 458

Grade 2 Braille, 1719

graphics, 405406, 409, 422, 423

grounds, electrical, 3538, 264

GUI (graphics user interface), 421, 422

H

half adder, 176177

halt, 360, 369, 373

hardware, computer

accessing, 419

defined, 311

logic gates and, 65

relays in, 63

software united with, 356

telegraphs and, 7

Harvard Mark I/II, 111, 184, 186, 187, 430

Haüy, Valentin, 13, 14

hertz, 217

Hertz, Heinrich Rudolph, 217

hexadecimal (base 16) system

ASCII/hex conversion, 153157

Baudot codes and, 150153

description of, 141148

moving from 8-bit to, 163

Unicode and, 163, 166

high-level languages, 394, 429441

Hilbert, David, 386

Hindu-Arabic number system, 9395

Hopper, Grace Murray, 430, 431

HTML (Hypertext Markup Language), 144, 159, 387, 404, 434, 454, 457

HTTP (Hypertext Transfer Protocol), 454455, 456

Humbert, Haze, viii

hypertext, 450, 454

I

IBM, 140, 158, 188, 312, 411, 420, 431

IBM PC, 419, 422, 423

IC (integrated circuit) chips, 192196

IEEE standards, 441, 442, 443

IMSLP (International Music Score Library Project), 458

incandescent lightbulbs, 21, 29

increments, 243, 350, 355, 369, 371

indexing, associative, 449

indirect addressing, 337, 343

infinite loops, 228

initialization, 383, 437

input/output (I/O) devices, 315316, 403412

inputs

adding machine, 171

AND gate, 7475, 89, 174

buffer, 88

devices, 67

frequency divider, 235

inverter, 215

NAND gate, 86

NOR gate, 84

OR gate, 78

propagation time, 194

relay, 7071

R-S flip-flop, 220225

telegraph, 62

instruction codes, 302, 304, 306, 311, 312, 315, 319. see also operation codes

instruction fetch, 360, 371

insulators, 27

integers, 211

integrated circuit/chip, 192196

Intel 8080

flags, 331

instructions, 319, 329

I/O ports, 406

microprocessors, 312, 318

operating system, 417

operation codes, 336351

registers, 336

text editor, 426

Intel 8087, 445

internet, the, vii, 451459

interrupt-driven I/O, 407

intersection of classes, 44, 47

inversion, 200, 202

Invert signal, 204

inverters

circuitry, 215

defined, 79

flip-flop, 268

function of, 87

OR gates plus, 84

rules governing, 80

3-input AND gates, 89

IP (Internet Protocol) address, 455

ISO/IEC 8859, 138

iterations, 384

J

Jacquard loom, 185, 186

JavaScript, vii, 433441, 457

Jobs, Steve, 421

Jordan, F. W., 219

JPEG, 409

JSTOR, 458

jump instructions, 381385, 387389, 426

K

Kemeny, John, 431

keyboard handler, 415416

keyboards, 406407, 420

keywords, 435

Kilby, Jack, 192

Kildall, Gary, 417

kilobytes, 283

knowledge, shared, 447448, 457458

Knuth, Donald, 440

Kurtz, Thomas, 431

L

labels, 386

language

code as, 3

high-level, 394, 429441

numbers as, 91

programming, 425430, 432433

written, 3, 14, 19, 140

Langue des signes Québécoise (LSQ), 3

latches, 225, 226, 269, 304, 335, 338, 347, 358

law of contradiction, 45

The Laws of Thought (Boole), 56

LEDs (light-emitting diodes), 29, 258266

Leibniz, Gottfried Wilhelm von, 42

level-triggered flip-flop, 220225, 229

lightbulbs, incandescent, 2122

lightning, 24

Line Feed code, 157158

Linux, 424

little-endien method, 163, 300, 313

logarithms, 123, 185

logic

ALU function, 323, 330, 331

Aristotelian, 4142, 46

electrical circuits as, 53

law of contradiction, 45

mathematical proving of, 42, 46

logic gates

adding with, 169182

ALU, 332

AND gates, 7475

connected relays as, 68, 7175

hardware and software and, 311

math + hardware as, 65

NAND gates, 8486

NOR gates, 8184

OR gates, 7678

rules governing, 80

silicon chip, 194

speed and, 376

technology progression of, 196

transistors for, 191192

XOR gates, 175176

Longfellow, Henry Wadsworth, 118

loops, 379, 381384, 389, 436, 439

M

MAC addresses, 453, 454

machine codes, 317319, 413414

Macintosh, 421422, 423

macOS, 422

mask patterns, 134136

The Mathematical Analysis of Logic (Boole), 90

mathematics

analytical geometry, 405

floating-point arithmetic, 441445

logic and, 42

logic gates and, 65

see also Boolean algebra

Mauchly, John, 188

megabytes, 284

memex, 449, 450

memory

accessing, 348

address, 273277, 282287, 293296, 337

ASCII and, 159

busses, 356

code and data as, 315, 319

constructing, 240

diode matrix, 261

early computer, 188

flip-flops for, 220225, 267274, 285

human, 267

labels, 386

sound, 411

storage, 267268, 411412

Unicode format, 164165

units of, 284285

video display, 403406

see also RAM arrays

memory-mapped I/O, 406

microphones, 409411

microprocessors, 312313, 318, 413, 414, 421. see also Intel 8080

Microsoft, 160, 419, 423, 432

mnemonics, 338, 425, 427, 428

modems, 452

modulation, 451452

modules, QR code, 132

Moore, Claudette, viiiix

Moore, Gordon E., 193

Moore’s laws, 193

Morse, Samuel Finley Breese, 7, 5759

Morse code

around corners, 3133, 38

binary, 12

communication via, 26, 149150

decoding tables, 711

letters and numbers in, 2, 5, 7

punctuation in, 5

scannable barcodes and, 127

telegraph transmission of, 59

translating, 78

undefined codes, 11

MOS 6502, 313

Motorola 6800, 313, 421, 428

mouse, 407408, 421

move immediate instructions, 339, 341, 369, 427

move instructions, 342, 346, 349, 366

MP3, 411

MS-DOS, 419, 422, 423

multiplexing, 257

multiplication, 323, 389395

multiplication tables, 97, 105, 111

music, digitized, 458

N

Nakashima, Akira, 68

NAND gates, 8490, 173174, 194, 195, 245247

nanoseconds, 195

NASA Jet Propulsion Laboratory, 125

negative numbers, 198, 199, 200, 206211, 442

Nelson, Ted, 450, 451, 454

nested loops, 379, 439

networks, 66

neutrons, 23

nibbles, 140, 160, 396, 397

NIC (network interface control), 453

nines’ complement, 198

Nixie tubes, 251252, 255

noise, 120

NOR gates

7402 chip, 195

clock building with, 249, 255256

flip-flop, 217220, 268

inputs/outputs, 87

subtraction with, 210

versatility of, 89

wiring, 8184

normalized format, 441, 442

NOT operators, 47, 54, 55, 79, 84

Noyce, Robert, 192, 195

NPN transistor, 189190

numbers/numbering

Braille, 18

counting, 92

dollar/number conversion, 298302

floating-point, 441445

language of, 91

Morse code, 5

Roman numerals, 9394

see also specific system by name

Nyquist, Harry, 410

O

O’Brien, Larry, ix

octal (base eight) numbering, 100105, 113114, 139141, 271

Ohm, Georg Simon, 27

ohms, 27, 39

Ohm’s Law, 2728, 39

ones’ complement, 200, 205, 308

operands, 42, 90

operating system, 412, 413424

operation codes, 302, 319, 329, 336344. see also control signals; instruction codes

OR (union of classes), 47, 48, 51, 54, 66

OR gates

clock building with, 255

inputs/outputs, 87, 116, 174175, 238

silicon chip, 195

symbol for, 173

transistor-based, 191

wiring, 7678

OR operators, 90, 324326

Organon (Aristotle), 41

oscillators, 216, 232, 235, 237, 263, 296, 368

outputs

adding machine, 171

AND gate, 7475

buffer, 88

devices, 67

frequency divider, 235

inverter, 215

NAND gate, 86, 174

NOR gate, 84

OR gate, 78, 174

relay, 7071

R-S flip-flop, 220225

telegraph, 62

overflow, 203204, 209, 402

P

packet switching, 451

Panchot, Joel, ix

parameters, 397

PARC (Palo Alto Research Center), 420

parity, 129

Pascal language, 432

Paterson, Tim, 419

patterns, QR code, 133136

PCM (pulse code modulation), 410

Pearson Education, Inc., x

period, oscillator, 217, 243

peripherals, 315, 403412

Perseverance rover parachute, 123126

petabytes, 285

phones, 423

pixels

color of, 144

compressing, 408409

video display, 403405, 420421

plain text files, 157158

PNG (Portable Network Graphics), 409

ports, I/O, 406

positional notation, 9497

possibilities, conveying, 120123

potential, 27, 28, 38

precedence codes, 19

prime number algorithm, 439

program counter, 348, 350, 351, 358, 360

programmers, 419, 428, 430

programs, computer, 317318, 387, 419, 425445

PROM chips, 416

propagation time, 194

protons, 23

punctuation, 5, 18

PUSH/POP instructions, 401

Q

QDOS (Quick and Dirty Operating System), 419

quaternary system, 105, 106, 108, 141

Quick Response (QR) code, 131138

R

RAM (random-access memory) arrays, 274287, 291295, 347, 350, 403

read/write memory, 273274

registers, 335353, 355, 356357

relays/repeaters

adding machine, 172, 178

cascaded, 7175

computers with, 183184, 186, 187

double-throw, 78

electrically triggered, 6869

series of, 7175

telegraph, 6263

wiring, 6788, 214

repetition, 379

reset, 368, 371, 414

resistors, electrical

earth as, 37

insulators, 2627

ohms measuring, 2829

wire length and, 3839, 61

resolution, 403

restart instructions, 407

RET statement, 395402

Revere, Paul, 118120

ripple counters, 237

Ritchie, Dennis, 423

ROM (read-only memory), 261262, 264, 416

ROM matrices, 373, 375, 376, 389

Roman numerals, 9394

rotate instructions, 394395

routers, 453, 455

routines, 395398

Royal Institution for Blind Youth, 13

R-S (Reset-Set) flip-flops, 220225

rules, mathematical, 4243

S

saving data, 225

scratchpad memory, 394

sectors, 412

Seemann, Mark, ix

selectors, 286287

semiconductors, 189

sentinels, 386

servers, 453, 457

sets, algebraic, 43

Shannon, Claude Elwood, 68, 90

shift codes, 19, 150153

Shockley, William, 189, 190

short circuits, 28, 278279

sieve of Eratosthenes, 439

sign bit, 209

signal amplification, 68, 88, 189

signals, control, 295, 355378

signed/unsigned numbers, 210211

silicon, 189, 190

silicon chips, 193

simple-to-complex operations, 394

sink, current, 264

Sinnott, Dierdre, ix

Siskel, Gene, 121122

software

compatibility, 433

defined, 311

hardware united with, 356

operating system, 412, 413424

solid-state electronics, 190, 412

sound, 409411

source, current, 264

source-code file, 427

speed, computing, 195, 376377, 420

stacks, 399402

statements, 428, 431, 435

static electricity, 2324

Stibitz, George, 183, 184

storage

LIFO, 401

memory, 267, 268, 411412

operating system, 416

see also memory

Stroustrup, Bjarne, 433

structured programming, 431

subroutines, 395398, 418

subtraction, 197211, 301, 302, 307, 308, 319323

sum bits, 170171, 173, 175, 177

SVG (Scalable Vector Graphics), ix

Swan, Joseph, 21

switches, electrical

binary codes and, 29

circuits to trigger, 6770

digital clock, 250

on/off diagram, 32

parallel line of, 5256, 66

relay, 63

series of, 50, 66, 7274

syllogisms, 41, 46

T

tablets, 423

tags, 434, 454

Takeover switch, 286, 287, 291

TCP/IP, 455

telegraph, the

bidirectional, 3133

computer hardware and, 7

invention of, 5861

relays/repeaters, 62

wire length for, 39

telephone system, 68

teletypewriters, 150, 152

ten, 92, 9497, 99

tens’ complement, 207

terabytes, 284

terminals, battery, 2526

text

changing case, 323327

character encoding, 149

editor, 426

memory for, 405406

plain text files, 157158, 159

word wrapping, 157158

Thompson, Ken, 423

Thomson, William, 184

Tide-Predicting Machine, 184

Torvalds, Linus, 424

touchscreen, 408

transistors, 189192, 265, 278281

transmission errors, 17

triggering relays, 6869

Triple-Byte Accumulator, 303306, 311, 312, 316

tri-state buffers, 280281, 292, 304, 308, 332, 346, 369

true/false values, 439440

TTL chips, 193, 239

TTL Data Book for Design Engineers, 194, 195, 239

Tukey, John Wilder, 116

tungsten, 22

Turing, Alan, 386, 387

Turing complete programs, 387

two, 12

two’s complement, 208, 210, 308

U

UI (user interface), 418, 420

unconditional jump, 382

underflow, 402

Unicode, vii, 163167

union of classes, 43, 47

UNIVAC (Universal Automatic Computer), 188

UNIX, 423424

unsigned numbers, 210211

UPC (Universal Product Code), 126131

URL (Uniform Resource Locator), 454455

V

vacuum tubes, 187, 191

Vail, Alfred, 7

video display, 403406, 408, 420421

VisiCalc, 420

volatile memory, 285, 403

Volta, Count Alessandro, 27

voltage, 27, 28, 3738

Von Neumann, John, 188

W

Watt, James, 29

web browsers, 456

websites, 454455

Wells, H. G., 447, 451, 457, 459

Wilson, Flip, 422

Windows, 160, 161, 423

wires

adding machine, 171172

communication around corners via, 38

connectivity via, 22, 26

flip-flop, 217220

internet, 452453

resistance and length of, 3839, 61

resistance and thickness of, 27

switches along, 23

triggering relays with, 6869

vacuum tubes, 187

Wirth, Niklaus, 432

words, bits comprising, 139, 140

World Encyclopedia, 447448, 458

Wozniak, Steve, 313

Write signals, 268273

WYSIWYG (What you see is what you get), 422

X

Xerox, 421

XOR gates, 175176, 204205, 250251

Z

Zuse, Conrad, 183

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