The LEO Computers

Only one LEO I computer ever existed, there were 10 LEO II computers and almost 40 standard LEO IIIs were installed around the UK and abroad.

Discover which LEO was purchased by which company here and find all the items in the archive that mention that particular LEO. 

Each generation of LEO was described using Roman numerals (LEO I, LEO II or LEO III) and then each individual machine was referred to in numerical sequence (e.g. LEO II/1). Click on the blue links to see all the items in the archive that relate to each LEO computer. (This is a work in progress. If no items relate to a LEO that you're interested in, please check back later.) With grateful thanks to the LEO Computers Society for the information contained in this page.

The very first LEO computer was built by J. Lyons & Co. for themselves and ran its first program in November 1951. Everything about the machine was experimental so the build wasn't declared 'finished' until 1953.

LEO I was a valve based machine and used mercury delay line storage.  Starting with the design of the Cambridge EDSAC, the LEO team made considerable changes to cater for (i) large data volumes both in and out and (ii) the requirement for the computer to be reliable, to work all day every day supporting a major business. 

John Daines of the LEO Computers Society comments: "It is inconceivable today that one computer could do all that work between late 1951 and the arrival of LEO II in 1957 WITH NO BACKUP!"

LEO II/1
The second LEO built was also developed by J. Lyons & Co. for themselves. Lyons always intended for there to be two machines for reliability reasons but by the time the first LEO was declared 'finished', they were able to make considerable changes to the computer's design and so the second generation of LEOs was begun. By this time, LEO I had many external users so Lyons decided to build LEOs for others too. LEO II/1 became operational in 1957.

LEO II was also valve based and also used mercury delay line storage.  Much of the processor was similar but a big increase in overall speed was achieved by interleaving the bits in the delay lines that had the effect of making the store nearly 4 times faster.  It was also developed to support magnetic drums and magnetic tape storage.  The last 4 LEO II machines used core storage.  On both LEO I and II, programs were fed in by a bootstrap program called the Initial Orders from punched cards.

LEO II/2 - ordered by WD & HO Wills Tobacco (later Imperial Tobacco) in 1956 
LEO II/3 - ordered by Stewarts & Lloyds, Corby (later British Steel) in 1958
LEO II/4 - ordered by Ford Motor Company in 1958
LEO II/5 - installed by LEO Computers Ltd in Hartree House in 1959 to operate to offer computer services to other companies
LEO II/6 - ordered by the UK Ministry of Pensions & National Insurance in 1959
LEO II/7 - ordered by British Oxygen Company (BOC) in 1960
LEO II/8 - ordered by Standard Motor Company in 1960
LEO II/9 - ordered by Ilford (Photo) in 1960
LEO II/10 - second LEO II order by WD & HO Wills Tobacco (later Imperial Tobacco) in 1961
LEO II/11 - second order for Ford Motor Company (Dagenham) in 1961

LEO III
LEO III was a new development, using new technology like transistors and core storage (that was 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.

Some flexibility in the instruction code was provided by implementing the Wilkes invention of defining the instruction code by intersecting values in a core lattice.

Standard LEO III computers had a store speed of 13.5 μsec, 326 machines were 2.6 μsec and 360 machines were 6.0 μsec.

LEO III/1 - installed by LEO Computers at Hartree House to expand the computer service bureau in 1962
LEO III/2 - installed at Rand Mines, Johannesburg in 1962
LEO III/3 - installed at Dunlop Rubber in 1962
LEO III/4 - installed by the London Boroughs (local authorities) 
LEO III/5 - installed at CA Vandervell (CAV / Lucas Industries) in 1963
LEO III/6 - installed at Shell-Mex & BP in 1963
LEO III/8 - installed at Tubemakers of Australia in 1963 in Sydney
LEO III/9 - installed by UK HM Customs & Excise in 1963
LEO III/10 - installed by the UK Board of Trade in 1963
LEO III/11 - installed by Smith & Nephew in 1963
LEO III/12 - an experimental LEO 326 machine for themselves installed in 1963 (having merged with English Electric to form English Electric LEO)
LEO III/13 - installed by British Oxygen Company (BOC) in 1964
LEO III/14 - installed by Shell-Mex & BP in 1964
LEO III/15 - installed by Shell Australia in Melbourne in 1964
LEO III/16 - installed by Kayser Bondor (hosiery manufacturer) in 1964
LEO III/17 - installed by the Manchester Corporation (Manchester City Council) in 1963
LEO III/18 - installed by Cerebos (salt manufacturer) in 1964 and later British Oxygen Company (BOC)
LEO III/19 - installed by the National Savings section of the GPO (General Post Office, later British Telecom) in 1964. The GPO went on to place the largest ever order of LEO computers in the mid 1960s. Their last LEOs, used for telephone billing, weren't switched off until 1981.
LEO III/20 - installed by Colonial Mutual Life Assurance in Melbourne in 1964
LEO III/21 - installed by Tote Investors in 1964
LEO III/22 - installed by HJ Heinz & Co. in 1964 then Renold Chains
LEO III/23 - installed by Dunlop Rubber in 1965
LEO III/24 - installed by Allied Suppliers Ltd in 1965 then Phoenix Assurance in 1970
LEO III/25- installed by the UK Inland Revenue in 1965
LEO III/28- installed by the Coventry Corporation (local authority) in 1965
LEO III/30- installed by Royal Bank of Scotland in Edinburgh in 1965
LEO III/32- installed by David Colville & Sons (later British Steel) in 1965
LEO III/33- installed by Phoenix Assurance in 1965
LEO III/35 - installed by South Western Gas Board in 1965
LEO III/37 - installed by British Insulated Callendars Cables (later Balfour Beatty) in 1965
LEO III/38 - installed by HM Dockyard in Portsmouth in 1965
LEO III/39 - installed by Ever Ready Co in 1965 (having previously been LEO III/90 below)
LEO III/40 - installed by Consolidated Glass in 1965
LEO III/42 - installed by Renold Chains in 1965
LEO III/45 - installed by Wedd Durlacher Mordaunt (stock exchange trading) in 1966
LEO III/48 - installed by HM Dockyards in 1966
LEO III/90 - installed by the National Data Processing (NDPS) section of the GPO in 1964
LEO III/94 - installed by the London Borough Management Service Unit in 1967

LEO 326 and beyond
LEO III developed into LEO 326 with a much faster processor, larger main memory, multiple input / output channels and additional instructions.  The LEO III / 326 instruction set was implemented using microcode, a Wilkes invention that allowed the flexibility to add instructions e.g. double-length arithmetic, as requirements changed.

It supported several “exotic” devices like postal order readers (via data transmission lines), Autolector to read-mark-sense documents at speed, Kimball tags for clothing retailers, and Uptime card readers to read 40 column telephone “trunk tickets” at 2,000 per minute for billing purposes.  There was the CLEO high level language, combining – unlike COBOL - the ability to express both technical and business requirements and that permitted the trade off between speed and accuracy of program development and minimisation of machine resources as the balance began slowly to swing towards people being the prime cost factor.

LEO III/26 - 326 machine installed by National Data Processing Service (NDPS) section of the GPO in 1965
LEO III/27 - 326 machine installed by Freemans (retail company) in 1965
LEO III/29 - 360 machine installed by Shell-Mex & BP in 1965
LEO III/31 - 360 machine installed by Shell-Mex & BP in 1965
LEO III/34- 326 machine installed by National Data Processing Service (NDPS) section of the GPO in 1965
LEO III/36 - 326 machine installed by National Savings section of the GPO in 1966
LEO III/41 - 360 machine installed by NHKG (iron works) in Ostrava, Czechoslovakia in 1966
LEO III/43 - 360 machine installed by HM Dockyard in 1966, replacing LEO III/38
LEO III/44 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1966
LEO III/46 - 326 machine installed by J. Lyons & Co. in 1966 and then by he National Data Processing (NDPS) section of the GPO
LEO III/47 - 326 machine installed by UDZ, Czechoslovakia in 1966
LEO III/49- 326 machine installed by Shell Australia in Melbourne in 1966
LEO III/51- 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1966
LEO III/55 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in Portsmouth in 1966
LEO III/56 - 360 machine installed by HM Dockyard in 1967
LEO III/58 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1966
LEO III/66 - 326 machine installed by the National Savings section of the GPO in 1969
LEO III/67 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1969
LEO III/68 - 326 machine installed by the National Savings section of the GPO in 1969
LEO III/69 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1969
LEO III/70 - 326 machine installed by the National Data Processing (NDPS) section of the GPO in 1969
LEO III/93 - 360 machine installed by VLD, Czechoslovakia in 1969

Date : 1951 to 1969

Related Topics:
This exhibit has a reference ID of CH66430. Please quote this reference ID in any communication with the Centre for Computing History.
 

The LEO Computers

Click on the Images 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