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. Hardware description 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 each. It adopted the then high 1 megahertz clock rate of the Pilot ACE. Input/output was via Hollerith 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 an 8192-word magnetic drum for main storage. To access any of the 256 tracks of 32 words, the drum had one group of 16 read and one group of 16 write heads, each group on independent moveable arms, each capable of moving to one of 16 positions. Access time was 15 milliseconds if the heads were already in position; an additional 35 milliseconds was required if the heads had to be moved. There was no rotational delay incurred when reading from and writing to drum. Data was transferred between the drum and one of the 32-word delay lines. 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. (The DEUCE at the University of New South Wales {UTECOM} had a Siemens M100 teleprinter attached in 1964, giving 10 characters per second input/output). Decca magnetic tape units could also be attached. The automatic multiplier and divider operated asynchronously (that is, other instructions could be executed while the multiplier/divider unit was 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 eight 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. The individual words of the quadruple registers were associated with an auto-increment/decrement facility. That facility could be used for counting and for modifying instructions (for indexing, loop control, and for changing the source or destination address of an instruction). Being a serial machine, access time to a