23
Logic gates, ferrite core memory and the valve computer
Earth parallel: 1873–1954 (the flat liquid crystal screen: about 1970). Goal: a machine that follows a stored list of orders and does in a second the sums of a room of clerks, with a keyboard to tell it and a screen to show the answer.
| ID | Achievement | About year |
|---|---|---|
| 23.01 | Typewriter and teleprinterletters struck by keys, and the same keys working a distant printer over a wire: the keyboard's first form | 72 |
| 23.02 | Desk calculating machinea box of geared wheels that adds, subtracts, multiplies and divides at the turn of a handle | 73 |
| 23.03 | Punched cards and tabulating machinefacts kept as holes in cards, and machines that sort and count them: a count of the whole island in weeks | 75 |
| 23.04 | Punched paper tape, its code, punch and readera message or a list of orders kept as rows of holes in a paper ribbon | 76 |
| 23.05 | Two-state numbers and the algebra of logicevery number written with two signs only, and every yes-or-no question worked out by rule: the mathematics the machines are built on | 78 |
| 23.06 | Relay calculatora room of relays that works through a long sum by itself, from a tape of orders | 80 |
| 23.07 | Crystal diodea tiny one-way gate for current: a metal point on a chip of crystal, with no filament to burn out | 82 |
| 23.08 | Cathode-ray tube screena display before the flat screen: a beam of electrons writes figures and curves on glowing glass | 83 |
| 23.09 | OR gateits output is on if either input is on | 84 |
| 23.10 | AND gateits output is on only if both inputs are on | 84 |
| 23.11 | NOT gateturns on into off and off into on | 84 |
| 23.12 | NOR gateOR followed by NOT: from this one gate alone every circuit of logic can be built | 85 |
| 23.13 | NAND gateAND followed by NOT: it too can build everything | 85 |
| 23.14 | XOR gateon if the two inputs differ: the heart of the adder | 85 |
| 23.15 | Flip-floptwo gates feeding each other hold one bit until they are told to change | 86 |
| 23.16 | Clock pulse generatora steady train of pulses makes every part of the machine step together | 86 |
| 23.17 | Adderadds two binary digits and a carry; a row of them adds whole numbers | 87 |
| 23.18 | Register and countera row of flip-flops holds a number, and counts pulses | 88 |
| 23.19 | Decoder and selector circuitspick one line out of many from a number: which store, which operation | 88 |
| 23.20 | Printed circuit board and plug-in unitthe wiring etched in copper on a board, and each circuit a unit that can be pulled out and changed | 88 |
| 23.21 | Stabilised power supply and cooling ⚠steady voltages for thousands of valves, and their heat carried away | 88 |
| 23.22 | Ferritea magnetic ceramic that does not conduct: pressed from metal oxides and fired | 88 |
| 23.23 | Magnetic drum storea spinning drum coated like tape holds thousands of numbers under rows of heads | 89 |
| 23.24 | Arithmetic unitregisters and adders that add, subtract, shift and compare on command | 89 |
| 23.25 | Ferrite core memorya tiny ring of ferrite on crossed wires holds one bit with no power: thousands woven into a mat make a fast store | 90 |
| 23.26 | Keyboardthe typewriter's keys send coded signals straight into the machine | 91 |
| 23.27 | Control unit and the stored programthe orders are kept in the same store as the numbers, and the machine fetches and obeys them one by one | 92 |
| 23.28 | Computer built with valvesa stored-program machine in the manner of the Manchester University Mark II: some thousands of valves do in a second what a room of clerks does in a day | 94 |
| 23.29 | Programmingan instruction code, a library of ready-made routines, and a simpler language that the machine itself turns into its code | 95 |
| 23.30 | Display drive circuitswitches that put the right voltage on each dot of a screen, row by row | 97 |
| 23.31 | LCD monitora flat screen of liquid crystal between two sheets of coated glass: the picture formed dot by dot, with almost no power | 100 |