Grace's Guide

British Industrial History

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English Electric Co: KDF9 Computer

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Note: This is a sub-section of the English Electric Co

KDF9 was an early British computer designed and built by English Electric, later English Electric Leo Marconi, EELM, later still incorporated into ICL, which became a part of Fujitsu in 2002. It first came into service in 1964 and the last was decommissioned in 1980 at the National Physical Laboratory.

The logic circuits of the KDF9 were entirely solid-state. The KDF9 used transformer-coupled diode-transistor logic, built from germanium diodes, about 20,000 transistors, and about 2,000 toroid pulse transformers (magnetic amplifiers). They ran on a 1 MHz clock that delivered two pulses of 250ns separated by 500ns, in each clock cycle. The maximum configuration incorporated 32K words of 48-bit core storage (192K bytes) with a cycle time of 6 microseconds.

Each word could hold a 48-bit integer or floating-point number, two 24-bit integer or floating-point numbers, six 8-bit instruction syllables, or eight 6-bit characters. There was also provision for efficient handling of double-word (96-bit) numbers in both integer and floating point formats. However, there was no facility for byte or character addressing, so that non-numerical work suffered by comparison. Moreover, there was no standard character set. Each I/O device type had its own more or less similar character set. Not every character that could be read from paper tape could be successfully printed, for example.

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