ICT 1301

The ICT 1301 and its smaller derivative ICT 1300 were early business computers from International Computers and Tabulators. Typical of mid-sized machines of the era, they used core memory, drum storage and punched cards, but they were unusual in that they were based on decimal logic instead of binary.

The 1301 was designed by an ICT and GEC joint subsidiary, Computer Developments Limited (CDL) at GEC's Coventry site.

The 1301 was the main machine in the line. Its main memory came in increments of 400 words of 48 bits (12 decimal digits) plus two parity bits. The maximum size was 2,000 words. It was the first ICT machine to use core memory.

Backing store was magnetic drum and optionally one-inch-, half-inch- or quarter-inch-wide magnetic tape. Input was from 80-column punched cards and optionally 160-column punched cards and punched paper tape. Output was to 80-column punched cards, line printer, and optionally to punched paper tape.

The machine ran at a clock speed of 1 MHz and its arithmetic logic unit (ALU) operated on data in a serial-parallel fashion—the 48-bit words were processed sequentially four bits at a time. A simple addition took 21 clock cycles; hardware multiplication averaged 170 clock cycles per digit; and division was performed in software.

The computer was announced in May 1960. The first customer delivery was in 1962, a 1301 sold to the University of London. About 150 to 200 of these machines were sold. One of their main attractions was that they performed British currency calculations (pounds, shillings and pence) in hardware. They also had the advantage of programmers not having to learn binary or octal arithmetic as the instruction set was pure decimal and the arithmetic unit had no binary mode, only decimal or pounds, shillings and pence. The London University machine was restored to working condition by a group of enthusiasts completing their task in 2012.

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