LEO Computers (J. Lyons "Lyons Electronic Office" UK) (1951)

LEO-1 Control Desk







LEO III Operating Installation (Right)

In October 1947, the directors of J. Lyons & Company, a British catering company famous for its teashops but with strong interests in new office management techniques, decided to take an active role in promoting the commercial development of computers.

In 1951 the LEO I computer was operational and ran the world's first regular routine office computer job.

The company LEO Computers Ltd was formed in 1954.

LEO II computers were installed in many British offices, including Ford Motor Company, British Oxygen Company and the 'clerical factory' of the Ministry of Pensions at Newcastle. LEO lll computers were installed in Customs & Excise, Inland Revenue, The Post Office and in Australia, South Africa and Czechoslovakia.

LEO Computers Ltd merged with the computer interests of English Electric in 1963 to form English Electric LEO, and later, English Electric Leo Marconi (EELM). Subsequent mergers eventually found LEO incorporated into ICL in 1968, whilst the Bureau operation, based at Hartree House, combined with Barclays to form Baric.

Information and Photos Courtesy of LEO Computers Society.

Visit their excellent Web Site: LEO Computers Society Home Page

About the LEO Computers Society

About the "Lyons Electronic Office" (LEO I)

The LEO I used 5,936 valves, plus another 300-400 in auxiliary equipment. The LEO used 64 mercury tubes for storage (twice the memory capacity of the EDSAC machine built in Cambridge). Each memory tube was 5 feet, four inches in length and weighed half a ton. The computer was controlled from a control panel, with several oscilloscopes set up to monitor contents of the storage area. The machine also had a speaker installed and programmers could hear the sounds generated as LEO performed certain calculations. The programmers became so accustomed to certain frequency variations, that they could detect something was wrong with a program by the sounds produced through the speaker. The programmers also used this speaker arrangement to generate some of the first "computer music."

The total power consumption of the LEO was 30,000 watts. The machine took up about 5,000 square feet of floor space in the Lyons facility. The designers of the LEO created 228 separate electronic assembly units which were attached to 21 separate racks. This modular design helped provide easier access to components during a period of equipment failure. The biggest problem with machine faults was the failure rate of valves (tubes). About 50 valves per week were being replaced at one point.

See Books on LEO computers


LEO-1 Control Desk (1951)

LEO 1 Control Desk Wide View

LEO-1 Operator Station

LEO-1 Decimal-Sterling Binary Converter

LEO II at WD&HO Wills

LEO III Engineer's Panel


LEO II Computer


LEO Computers Society

LEO Computers Society

Membership in the LEO Computers Society is open to all ex-employees of LEO Computers and its succeeding companies, and anyone who worked on a LEO computer. The Society maintains a web site with fascinating information on the unique history of the LEO computers.

The Society also sponsors reunions of those who worked with or on the early LEO computers.

Their web site contains photos and charts of locations of early LEO computers.

For information on memberships, contact: Peter Byford, Chairman, LEO Computers Society - pgb@bcs.org.uk









Books About the LEO Computers

LEO : The First Business Computer
by Peter J. Bird
The first book to tell the story of J. Lyons' pioneering work in moving computers out of the laboratory and into the office. This illustrated history gives the background of how the company was founded as well as details of the development of Leos I, II & III, with many technical appendices giving various features of the machines. Published by Hasler Publishing Ltd.
ISBN 0-9521651-0-4

The World's First Business Computer

by David Caminer, John Aris, Peter Hermon, Frank Land
The story of how the Leo came to be developed, with individual accounts of some of the earliest jobs written by the consultants who brought them to fruition. The authors were all part of the group that put LEO, the first business computer to work. Published by McGraw-Hill. ISBN 0-07-709236-8


Other References on LEO Computers


Aris, J.B.B., (1998), Inventing Systems Engineering, Proceedings of the Kyiv Symposium, Kyiv, 1998.

Caminer, D.T., Aris, J.B.B., Hermon, P.M.R., Land, F.F., (1996), User-Driven Innovation: The World's First Business Computer, McGraw-Hill, Maidenhead, UK (Note this is the UK edition)

Caminer, D.T., Aris, J.B.B., Hermon, P.M.R., Land, F.F., (1998), "LEO: The Incredible Story of the World's First Business Computer", McGraw-Hill, New York. (Note this is the US edition )

Simmons, JRM, (1962), LEO and the Managers, MacDonald, London

Papers and Reports

Aris, J.B.B., (2000), Inventing Systems Engineering, IEEE Annals of the History of Computer Science, Summer.

"Hendry, J., (1987), The Teashop Computer Manufacturer: J. Lyons and the Potential and Limits of High-Tech Diversification" Business History, Vol.XXIX, No. 1, Jan., pp.73-102."

Land, F.F. (1998), LEO, the First Business Computer: A Personal Experience, in Glass, R.L., (ed)., In the Beginning: Recollections of Software Pioneers, IEEE Computer Society, Los Alamitos, California, pp 134-153

Land, F. F. (2000), The First Business Computer: A Case Study in User-Driven Innovation, IEEE annals of the History of Computer Science, Summer

Thompson, T.R. and Standingford, O., (1947), Report on Visit to USA, May/June 1947, archives of J. Lyons and Co.


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