CHAPTER 21

ACE

martin campbell-kelly

I

n October 1945 Alan Turing was recruited by the National Physical Laboratory to lead

computer development. His design for a computer, the Automatic Computing Engine

(ACE), was idiosyncratic but highly effective. The small-scale Pilot ACE, completed in

1950, was the fastest medium-sized computer of its era. By the time that the full-sized ACE

was operational in 1958, however, technological advance had rendered it obsolescent.^1

Introduction

Although the wartime Bletchley Park operation saw the development of the electromechanical

codebreaking bombe (specified by Turing) and the electronic Colossus (to which Turing was

a bystander), these inventions had no direct impact on the invention of the electronic stored-

program computer, which originated in the United States.

The stored-program computer was described in the classic ‘First draft of a report on the

E D VA C ’,^2 written by John von Neumann on behalf of the computer group at the Moore School

of Electrical Engineering, University of Pennsylvania, in June 1945. The report was the out-

come of a series of discussions commencing in the summer of 1944 between von Neumann

and the inventors of the ENIAC computer—John Presper Eckert, John W. Mauchly, and others.

ENIAC was an electronic computer designed primarily for ballistics calculations: in practice,

the machine was limited to the integration of ordinary differential equations and it had several

other design shortcomings, including a vast number of electronic tubes (18,000) and a tiny

memory of just twenty numbers. It was also very time-consuming to program. The EDVAC

design grew out of an attempt to remedy these shortcomings. The most novel concept in the

EDVAC, which gave it the description ‘stored program’, was the decision to store both instruc-

tions and numbers in the same memory.

It is worth noting that during 1936 Turing became a research student of Alonzo Church at

Princeton University. Turing came to know von Neumann, who was a founding professor of

the Institute for Advanced Study (IAS) in Princeton and was fully aware of Turing’s 1936 paper

‘On computable numbers’. Indeed, von Neumann was sufficiently impressed with it that he

invited Turing to become his research assistant at the IAS, but Turing decided to return to