ICT 1301

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 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, 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 4 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.

It was announced in May 1960. The first customer delivery was in 1962, a 1301 sold to the University of London. In total 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 still exists (January 2006) and is being reinstated to working condition by a group of enthusiasts.

A typical 1301 requires 700 square feet (65 square metres) of floor space and weighs about 5 tons. It consumes about 13kVA of three-phase electric power. The electronics consist of over 4,000 printed circuit boards each with many Germanium diodes (mainly OA5), Germanium transistors (mainly Mullard GET872), resistors, capacitors and inductors. It contains no integrated circuits, though it does have a handful of thermionic valves and a few dozen relays which work only at human speed when buttons are pressed.

tandard Peripherals

The card reader was capable of reading 600 cards per minute, each with 80 columns containing one character or a space.

The card punch could punch 100 cards per minute, again each card had 80 columns containing one character or a space.

The line printer could print 600 lines per minute. It used a print barrel made up of 120 print wheels each with 50 characters around its edge. Each of the 120 print positions had a print hammer which when fired squeezed the paper and an inked ribbon between itself and the rotating print barrel for a fraction of a second.

The drum could record 12,000 words of data. It also had 400 words of 'reserved' storage where the computer's bootstrap program (called Initial Orders) was stored. Up to 8 drums could be attached. Average access time was 5.7 ms.

Optional Peripherals

The 'standard' magnetic tape system (called tape type 3) used half inch (12.7mm) wide magnetic tape with ten tracks at a density of 300 bits per inch. Four of the tracks held data, four more tracks held the inverse of the data and there was a parity bit for both groups of four. This allowed single bit errors to be corrected and double bit errors to be detected. Up to eight Ampex TM4 tape decks could be connected and each ran at 75 inches per second, giving a throughput of 22,500 digits per second. Spools could hold up to convert|3600|ft|m of tape and were of the three prong design not the later industry standard expanding hub design.

The 'High Speed' magnetic tape system (called tape type 1) used one inch (25.4mm) wide magnetic tape with sixteen tracks at a density of 300 bits per inch. Eight of the tracks held data and eight more tracks held checking data. This allowed single bit errors to be corrected and double bit errors to be detected. Up to eight tape decks could be connected and each ran at 150 inches per second, giving a throughput of 90,000 digits per second. Spools could hold up to convert|3600|ft|m of tape and were of the three prong design common at the time for professional audio and video recorders.

One or two paper tape readers could be connected, each with a speed of 1,000 characters per second.

A paper tape punch of 300 characters per second was available.

An online teleprinter was available, though very few machines had these.

Towards the end of the working life span of the 1301, a single ICT standard interface could be added to allow data to written to the by then industry standard magnetic tape.

ICT 1300

The ICT 1300 was identical to the 1301 in every way except that its card reader was limited to 300 cards per minute and its line printer was limited to 300 lines per minute. It tended to be sold with less core storage and drum storage and without magnetic tape. A drum with only a quarter of the read/write heads fitted was commonly used giving just 3,000 words of 48 bits as backing storage.

External links

* [http://ict1301.co.uk/13012006.htm ICT 1301 resurrection project] This is "Flossie" the original machine sold to London University.
* [http://milsom.mysite.orange.co.uk/1301/1301f.htm Pictures of the ICT 1301]
* [http://www.cs.nott.ac.uk/~ef/ComputerXHistory/FirstComputers-2/1961-ICT1301-GeneralView.htm Picture of one of the prototype ICT 1301s]


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