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Elliott 920M Computer

Technical Information

Catalogue No: C0005
Category: General Purpose
Object Type: Signal/Data Processor
Object Name: Elliott 920M Computer
Part No: MCS920M/IL322A11787
Serial No: 88
Manufacturer: Marconi-Elliott Computer Systems
Division: Unknown
Platform(s): Jaguar
Year of Manufacture: circa 1982
Dimensions: Width (mm): 190
Height (mm): 190
Depth (mm): 360
Weight (g): 14,380
Location: On Loan

Marconi-Elliott Computer Systems Ltd.
Title. MCS920M Digital Computer
Catalogue No. MCM7
Drawing No. IL322A11787
NATO No. 6JA-7440-99-111-8581
Serial No. 88
Joint Services Manuf. No. K0978
Borehamwood England
A General Electric Company


This Unit is Serial No. 88 and was made at Borehamwood in 1982.

In July 2019 this Computer was donated on permanent Loan to the The National Museum of Computing.

In 1967 Elliotts had been awarded a major contract for the design, development and integration of a Navigation and Weapon Aiming Sub-System (NAVWASS) for the RAF's new Jaguar aircraft.

The Jaguar was designed as a close air support aircraft for supporting ground troops in daylight. The NAVWASS enabled the pilot to navigate and fly at low level and high speed to acquire and accurately attack targets. Trials of the prototype Jaguar system were carried out using a Varsity aircraft at West Malling airfield in Kent


The Jaguar NAV/WASS  sub-system comprises four principal groups of equipment. The sensors, which measure what the aircraft is doing and feed these measurements into the computer; the computer sub-system which processes this measured information into a form which can be used by the pilot; the cockpit controls which control the system's mode of operation and lastly, the cockpit displays which show to the pilot the computer's outputs of converted measurement information and also information, such as target or waypoint position, which is being input into the computer. The system included an E3R inertial platform, Digital Computer, a HUD, Projected Map Display, Horizontal Situation Indicator and various cockpit control panels.

The 920 series of computers was developed at Elliotts Borehamwood Computing Division in the 1960’s and was derived from the successful 901 commercial computer which was miniaturised for airborne use. One of the primary production derivatives was the MCS 920M which was used in the
Jaguar Navigation and Weapon Aiming Sub-System NAVWASS This system comprised the MCS920M central digital computer, E3R inertial platform, projected map display and horizontal situation indicator together with the necessary power supply, electronic, interface and control units.
The MCS 920M is a microminiature general purpose digital computer using flat pack integrated circuits and. has a random access, 8192 word, 18 bit ferrite core store with a 2microsecond cycle time. Elliotts lacked access to multi-layer printed circuit board technology so used a special technique developed at the Borehamwood Computer Laboratory (see ‘Moving Targets’ by Simon Lavington). The box is unusual in that it folds out into three blocks.
In addition to performing navigation and weapon aiming calculators, the computer caters for in-flight monitoring, initial alignment and in situ first line system testing. The Computer also had an Interface Unit which enables the digital computer to receive and transmit information from and to other units in the aircraft in compatible signal form. The Interface Unit also supplied the power for the computer and Navigation Control Unit.
In its production form the MCS920M was widely used in its intended role in the Jaguar navigation attack system and eventually grew to a 64 K machine. The 920M also saw use in the ELDO rockets.
The MCS920M was also adopted for a number of naval inertial navigation applications.

Thanks to Terry Froggatt we have two pages of how a 920M is built.

The two pages shown look very like the Core Stack photos (minus a top plate) catalogued as C1059.

We assume an Elliott typo (not uncommon), for "7 epoxy-glass printed circuit boards" read "9 epoxy-glass printed circuit boards" There are 24 chips in the Core Stack and a pair of 24-way ribbon cables. Possible explanation:

“8192 words is not a square number. On a 920B/903 the store is addressed as two 4096-word stores, so there are 64 "Y" address wires running though ALL 8192 words, and 64 "X" address wires running through EACH 4096 words.

Total 192 wires, = 24 * 8, (and each wire needs 4 diodes).

So, your core store may well be a spare for a 920M, or perhaps from a 920M "extra store" module, or a 920C.


See:    http://www.computerconservationsociety.org/software/elliott903/more903/Manuals/index.htm  this gives copious links to the 920 Computer family.

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