In October 1947, the directors of J. Lyons & Co., a London based catering company, famous for its teashops but with strong interests in new office management techniques, decided to build their own digital computer.
Lyons Electronic Office (LEO I) went operational in 1951 and it is regarded as the world’s first computer to run a regular routine office computer job.
LEO I was modelled on the Electronic Delay Storage Automatic Computer (EDSAC) built by Maurice Wilkes and his team at the University of Cambridge. In 1947 the project at Cambridge was supported by Lyons with economical means and the services of an assistant, employed by the company. In return, guidance could be given on how Lyons could develop its own electronic calculator.
LEO I had twice the memory size of EDSAC, with 64 mercury delay tubes. More than 6,000 thermionic valves were used. The entire machine occupied 5,000 square feet, with air-conditioning.
Payroll automation was one of the main objectives of Lyons. After further work on the machine’s reliability, in 1953 the goal was achieved. An experienced clerk usually took about eight minutes to calculate one employee’s weekly pay: LEO I managed to do the same operation in 1.5 seconds.
The success of the LEO I prototype led to the development of LEO II and LEO III: in 1954 LEO Computers Ltd. was established.
LEO II design followed essentially the same methods used for LEO I, but several changes were made. These included improving the store cycle speed to nearly four times that of LEO I by decreasing the dimensions of the mercury delay tubes. In the later models of LEO II, storage architecture was improved by use of ferrite core storage; and transistors were used for the first time in some circuitry.
LEO II computers were installed in many British offices, including Ford Motor Company, British Oxygen Company and offices of the Ministry of Pensions & National Insurance. A full list of LEO II installations can be found here.
LEO III was the solid-state successor to the earlier LEO I/II valve-based range. It was fully transistorised, using over 100,000 transistors and semiconductor diodes.
A new program language was devised for use with LEO III: it was based on Cobol and named Clear Language for Expressing Orders (CLEO). LEO III computers were installed in Customs & Excise, Inland Revenue, The Post Office and in Australia, South Africa and Czechoslovakia. A full list of LEO III installations can be found here.
In 1963, LEO Computers Ltd merged with the computer interests of English Electric to form English Electric LEO, and later, English Electric Leo Marconi (EELM). In 1963, subsequent mergers eventually found LEO incorporated into International Computers Limited (ICL) a large British computer hardware, computer software and computer services company, operating until 2002.