Marconi Myriad

The Marconi Myriad was an early computer designed by the Marconi Company in the 1960s and assembled in the same factory as the English Electric System 4/30.

Myriad was a 24-bit machine largely built using integrated circuits from Ferranti which were packaged in small "TO8" type cans. The architecture was "conventional", and was developed largely by the in-house Marconi team that designed similar, but physically larger computers based on SB345 discrete surface-barrier transistors. These machines were used successfully by the Royal Radar Establishment (RRE) in the UK. In Sweden they were used by the Government in their "Fur Hat" defence system and in the Air Force where two computers were used for the meteorological service from late 1960s to early 1990s. They also provided flight data for UK military air traffic control for 15 years. In Australia, two Myriads were used as part of each of the AF/TPS-802 "HUBCAP" air-defence systems from 1967–97. The Myriads were used in a coupled mode with one providing a radar data extractor and data quantiser role, and the other driving display overlays and tactical display information on radar and tactical screens.

The Myriad 1 computer was mounted in a small desk format, and was far smaller than any comparable machine at the time. Eight bit paper tape was (somewhat) standard input (the software could handle data input in either the ASCII or the rather idiosyncratic KDF9 character codes) – but a high speed 1000-characters per second electrostatic reader made by Facit was capable of projecting paper tape across a room in spectacular fashion. A high-speed printer was provided. The major machine cycle time was around 800 nanoseconds, with inner cycles around 200 nanoseconds.

Most early programming was performed in very amenable and complete assembly code. Some use was also made of a subset of Coral 66 known as Mini-Coral. The 24-bit architecture provided a logical and flexible address/data environment but the 15-bit address limited the memory size to 32K 24-bit words. The operating system allowed multiple programs to run concurrently but most systems were coded "on the bare metal". Addressing allowed easy integration of external computing and display equipment. An embedded parallel bus allowed two Myriads and some peripheral expansion devices to be directly addressed. For example, in the "Hubcap" configuration, two 16k Myriads shared a 32k 4-wire core memory "backing store" and could save, retrieve or share information at high speed.

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