Terry Froggatt's Home Page

Elliott Computers

Here is my detailed description of the MCM7 variant of the Elliott 920M, largely written during Covid lockdown.

Here is my 2018 implementation of BCPL for the Elliott 900 Series computers.

Here is my report on my visit to the National Museum of Scotland's Collection Centre in 2014, to inspect their brace of Elliott 903s, including photographs and lists of their paper tapes.

Here is my description of the Elliott 900 Series computers, written for the Computer Conservation Society in 2004:


WORD Format

PDF Format

Chapter 1: Delivery List and Applications



Chapter 2: Systems Architecture



Chapter 3: Instruction Set and Times



Chapter 4: Software and Sample Programs



Chapter 5: List of References



(Total size of five individual files)



Single ZIP file of all five Chapters



and the explanatory notes which I wrote at the time are here.

My own Elliott computer is an "Arch 9000", which is really a 920B or a 903, but in a different box, and with a re-arranged control panel. This photograph shows most of the computer. (The processor and 8192-word store are in the centre rack, the extra 8192-word store is to the left, and the paper-tape logic and power supplies are to the right). Here are close-ups of that control panel, and of an A-GL card (initial instructions) and an A-FA card (one of 18 identical cards each holding a bit of each register).

The text of a brief talk which I gave at the Computer Conservation Society's Elliott seminar, at the Science Museum in London in May 2008, is here, although I didn't read out the final page describing the demonstrations at the seminar.

A scan of the Elliott document "903/905/920 Useful Notes" is here. This describes the various codes used to represent text on paper tape, and it explains one of the formats used on binary tapes that were to be read by initial instructions.

I have two Flexowriters, a grey one and a brown one, seen together from the left and right. Both use the paper-tape code described in "903/905/920 Useful Notes" as 920 (or 503) Telecode, rather than using the ASCII tape code. I did once have a third Flexowriter which I gave to Tony Sale at Bletchley Park as a spare for his rebuilt Colossus.

For the person with a potentially working Elliott 920B or 903 of their own, but who doesn't have a register display unit to help locate the problems, (there is at least one such), here are some notes about how to build your own.

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