English Electric DEUCE

English Electric DEUCE

The DEUCE (Digital Electronic Universal Computing Engine) was one of the earliest British commercially available computers, built by English Electric from 1955.

It was the production version of the Pilot ACE, itself a cut down version of Alan Turing's ACE.

The DEUCE had 1450 thermionic valves, and used mercury delay lines for its main memory; each of the 12 delay lines could store 32 instructions or data words of 32 bits. It adopted the then high 1 megahertz clock rate of the Pilot ACE. Input-output was via 80-column punch card equipment. The reader read cards at the rate of 200 per minute, while the card punch rate was 100 cards per minute. The DEUCE also had a 8192-word magnetic drum for main storage. The DEUCE could be fitted with paper tape equipment ; the reader speed was 850 characters per second, while the paper tape output speed was 25 characters per second. Magnetic tape units could also be attached. The automatic multiplier and divider units operated synchronusly (that is, other instructions could be executed while the multiplier and divider units were in operation). Two arithmetic units were provided for integer operations: one of 32 bits and another capable of performing 32-bit operations and 64-bit operations. Auto-increment and auto-decrement was provided on 8 registers from about 1957. Array arithmetic and array data transfers were permitted. Compared with contemporaries such as the Manchester Mark 1, DEUCE was about ten times faster.

Programming the DEUCE involved added complication, as each instruction had to wait its turn in the delay line – the position of instructions in the store greatly affected performance. Reading data from a card reader was done in real-time – each row had to be read as it passed the read brushes, without stopping. Similarly for the card punch. The normal mode of reading and punching was binary. Decimal input and output was performed via software.

The front panel of the DEUCE featured two CRT displays: one showed the current contents of registers, while the other showed the content of any one of the mercury delay line stores.

The first three machines were delivered in the spring of 1955; in late 1958 a DEUCE Mark II improved model appeared. This version employed a combined card reader and punch. The combined reader and punch behaved like the separate units on the earlier DEUCE Mark I machines; however, it was provided with hardware conversion of decimal data to BCD on input, and vice versa on output. Data could be read in and punched simultaneously at 100 cards per minute. The DEUCE Mark IIA provided seven extra mercury delay lines, each of 32 words.

A total of 33 DEUCE machines were sold between 1955 and 1964.[1]

  1. ^ Copeland, B. J., ed., Alan Turing's Automatic Computing Engine, Oxford: Oxford University Press, 2005, ISBN 0-19-856593-3

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