A1. Turing's universal machine

Year: 1936
Zone: Logic, Theory & Cryptography
Band: inner
Tier: Built

Alan Turing, 1936: a tape, a head and a table of rules can carry out any computation. This machine adds 1 to a binary number. Step it and watch the carry ripple left.

PaperOn Computable Numbers, 1936
ACE designNPL, 1945/46
Imitation Game1950

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Binary incrementer · state scan · step 0

1011

Transition rules
State	Read	Write	Move	Next
scan	0	0	R	scan
scan	1	1	R	scan
scan	blank	blank	L	carry
carry	1	0	L	carry
carry	0	1	L	halt
carry	blank	1	L	halt

The whole program is the six-row table. Turing's insight was that the table itself can be written on the tape, so one universal machine can run any table. That is software.

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