Programming ENTER:
Christopher Strachey's Draughts Program
David Link

This article details some problems – and some solutions – encountered when resurrecting a program for the game of draughts from 1951 on an emulator of the Ferranti Mark I.

The Ferranti Mark I was the industrial version of the Manchester Mark I, whose prototype, the Manchester "Baby" (SSEM), performed its first calculation on 21st June 1948. The algorithm here described was one of the earliest complex applications authored on the pioneer computer that did not only serve system testing purposes. Christopher Strachey, an outsider to the Manchester computer laboratory and a school teacher, had developed the software in his spare time. Martin Campbell-Kelly writes, relying on the oral histories from lab personnel:

"Strachey sent his programme [draughts] for punching beforehand. The programme was about 20 pages long (over a thousand instructions), and the naivete of a first-time user attempting a programme of such length caused not a little amusement among the programmers in the laboratory. Anyway, the day came and Strachey loaded his programme into the Mark I. After a couple of errors were fixed, the programme ran straight through and finished by playing God Save the King on the hooter (loudspeaker). On that day Strachey acquired a formidable reputation as a programmer that he never lost."

David Link, Programming ENTER. Christopher Strachey's draughts program. Resurrection 60 (2012/3): 23-31.

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