Home > LEO Computers > Lyons Electronic Office (LEO) Archive > CCH LEO Artefacts Collection > Leo III Board

Leo III Board

 Home > LEO Computers > Lyons Electronic Office (LEO) Archive > CCH LEO Artefacts Collection > Leo III Board

One of the many boards that would have been installed in a LEO III computer.

Board no: E3/2 508

The first LEO III was completed in 1961. This was a solid-state machine with a ferrite core memory. It was micro-programmed and was controlled by a multi-tasking operating system. LEO III was a new development, using new technology like transistors and core storage, allowing it to be much larger in capacity than LEO I and II. It had no magnetic drums or discs. It was a parallel machine with 40 bit adders, data paths and routes to autonomous input / output channels that avoided loading the central processor. Programs were loaded from magnetic tapes and there was an operating system, called the Master Routine, to allocate resources to programs, control the key facility of multi-programming (several programs in store but only one active at any instant in time with each program protected from interfering with another) and to provide an interface for the operators to deal with job initiation and any error conditions.
In 1963 LEO Computers Ltd was merged into English Electric Company and this led to the breaking up of the team that had inspired LEO computers. English Electric Company continued to build the LEO III, and went on to build the faster LEO 360 and even faster LEO 326 models, which had been designed by the LEO team before the takeover.
All LEO IIIs allowed concurrent running of as many as 12 application programs through the Master program operating system. Some were still in commercial use in British Telecom until 1981. Many users fondly remember the LEO III and enthuse about some of its quirkier features, such as having a loudspeaker connected to the central processor which enabled operators to tell if a program was looping by the distinctive sound it made.

Manufacturer: LEO Computers LTD
Date: 1961

Comment on This Page

Other Systems Related To Leo III Board:

Item Manufacturer Date
Leo II Valve Rack LEO Computers LTD June 1959
Leo III Logic Board LEO Computers LTD early 1960s
Leo III Digital Clock LEO Computers LTD 1961
55625 Program Wiring Subset Unit from LEO III LEO Computers Ltd c1965

This exhibit has a reference ID of CH70740. Please quote this reference ID in any communication with the Centre for Computing History.


Leo III Board

Click on the Image(s) For Detail


Help support the museum by buying from the museum shop

View all items

Founding Sponsors
redgate Google ARM Real VNC Microsoft Research
Heritage Lottery Funded
Heritage Lottery Fund
Accredited Museum