LEO (computer)

The LEO I (Lyons electronic office I) was the first computer used for commercial business applications.

The prototype LEO I was modelled closely on the Cambridge EDSAC. Its construction was overseen by Oliver Standingford, Raymond Thompson and David Caminer of J. Lyons and Co. LEO I ran its first business application in 1951. In 1954 Lyons formed LEO Computers Ltd to market LEO I and its successors LEO II and LEO III to other companies. LEO Computers eventually became part of English Electric Company (EELM) where the same team developed the faster LEO 360 and even faster LEO 326 models. It then passed to International Computers Limited (ICL) and ultimately Fujitsu.

LEO series computers were still in use until 1981.[1]

Origins and initial design

J. Lyons and Co., one of the UK's leading catering and food manufacturing companies in the first half of the 20th century, sent two of its senior managers, Oliver Standingford and Raymond Thompson, to the USA in 1947 to look at new business methods developed during World War II. During their visit they met Herman Goldstine, one of the original developers of ENIAC, the first general-purpose electronic computer (although it had no stored program). Standingford and Thompson saw the potential of computers to help solve the problem of administering a major business enterprise. They also learned from Goldstine that, back in the UK, Douglas Hartree and Maurice Wilkes were actually building another such machine, the pioneering EDSAC computer, at the University of Cambridge.[2]

On their return to the UK, Standingford and Thompson visited Hartree and Wilkes in Cambridge, and were favourably impressed with their technical expertise and vision. Hartree and Wilkes estimated that EDSAC was twelve to eighteen months from completion, but said that this timeline could be shortened if additional funding were available. Standingford and Thompson wrote a report to the Lyons' board recommending that Lyons should acquire or build a computer to meet their business needs. The board agreed that, as a first step, Lyons would provide Hartree and Wilkes with £2,500 funding for the EDSAC project, and would also provide them with the services of a Lyons electrical engineer, Ernest Lenaerts. EDSAC was completed and ran its first program in May 1949.[3]

Following the successful completion of EDSAC, the Lyons' board agreed to start the construction of their own machine, expanding on the EDSAC design. The Lyons machine was christened Lyons Electronic Office, or LEO. On the recommendation of Wilkes, Lyons recruited John Pinkerton, a radar engineer and research student at Cambridge, as team leader for the project. Lenaerts returned to Lyons to work on the project, and Wilkes provided training for Lyons' engineer Derek Hemy, who would be responsible for writing LEO's programs. On 15 February 1951 the computer, carrying out a simple test program, was shown to HRH Princess Elizabeth.[4] The first business application to be run on LEO was Bakery Valuations. This was successfully run on 5 September 1951,[4] and LEO took over Bakery Valuations calculations completely on 29-30 November 1951.[5][4]

Technical description

LEO I's clock speed was 500 kHz, with most instructions taking about 1.5 ms to execute.[6][7][8] To be useful for business applications, the computer had to be able to handle a number of data streams, input and output, simultaneously. Therefore, its chief designer, John Pinkerton, designed the machine to have multiple input/output buffers. In the first instance, these were linked to fast paper tape readers and punches, fast punched card readers and punches, and a 100 line a minute tabulator. Later, other devices, including magnetic tape, were added. Its ultrasonic delay line memory based on tanks of mercury, with 2K (2048) 35-bit words (i.e., 834 kilobytes), was four times as large as that of EDSAC. The systems analysis was carried out by David Caminer.[9]

Applications and successors

Lyons used LEO I initially for valuation jobs, but its role was extended to include payroll, inventory, and so on. One of its early tasks was the elaboration of daily orders which were phoned in every afternoon by the shops and used to calculate the overnight production requirements, assembly instructions, delivery schedules, invoices, costings, and management reports. This was the first instance of an integrated management information system.[10] The LEO project was also a pioneer in outsourcing: in 1956, Lyons started doing the payroll calculations for Ford UK and others on the LEO I machine. The success of this led to the company dedicating one of its LEO II machines to bureau services. Later, the system was used for scientific computations as well. Met Office staff used a LEO I before the Met Office bought its own computer, a Ferranti Mercury, in 1959.[11]

In 1954, with the decision to proceed with LEO II and interest from other commercial companies, Lyons formed LEO Computers Ltd.


The first LEO III was completed in 1961. This was a solid-state machine with a 13.2 μs cycle time ferrite core memory. It was microprogrammed and was controlled by a multitasking operating system. 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, primarily producing telephone bills, purchased in the mid- to late 1960s, were still in commercial use with GPO Telephones, forerunner of British Telecom, until 1981, remaining usable throughout, using parts cannibalised from redundant LEOs purchased by the GPO.

Users of LEO computers programmed in two coding languages: Intercode,[12] a low-level assembler type language; and CLEO (acronym: Clear Language for Expressing Orders), the COBOL equivalent.

One of the features that LEO III shared with many computers of the day was a loudspeaker connected to the central processor which enabled operators to tell whether a program was looping by the distinctive sound it made.[13] Another quirk was that many intermittent faults were due to faulty connectors and could be temporarily fixed by briskly strumming the card handles.

English Electric LEO Computers, later English Electric Leo Marconi (EELM), eventually merged with International Computers and Tabulators (ICT) and others to form International Computers Limited (ICL) in 1968. In the 1980s, there were still ICL 2900 mainframes running LEO programs, using an emulator written in ICL 2960 microcode at the Dalkeith development centre.[14] At least one modern emulator has been developed which can run some original LEO III software on a modern server.[15]


Whether its investment in LEO actually benefited J. Lyons is unclear. Nick Pelling notes that before LEO I the company already had a proven, industry-leading system using clerks that gave it "near-real-time management information on more or less all aspects of its business", and that no jobs were lost when the system was computerized. In addition, LEO Computers lost money on many of its sales because of unrealistically low prices, forcing J. Lyons to subsidize it.[16]

See also


  1. "Leo III Installations". Leo Computers Society. Retrieved 28 March 2013.
  2. Ferry (2003), Chapter 2
  3. Ferry (2003), Chapter 3
  4. Bird, Peter John (1994). LEO: The First Business Computer. Hasler. pp. 84, 86, 228. ISBN 9780952165101.
  5. Ferry (2003), Chapter 4
  6. The Staffordshire University Computing Futures Museum LEO Page Archived 23 January 2012 at the Wayback Machine
  7. World's First Business Computer, LEO, Turns 60, TechWeek Europe
  8. Research, United States Office of Naval (1953). A survey of automatic digital computers. Office of Naval Research, Dept. of the Navy. p. 58.
  9. Williams, Christopher (10 November 2011). "How a chain of tea shops kickstarted the computer age". The Daily Telegraph.
  10. Frank, Land. "The story of LEO – the World's First Business Computer". Warwick University - Modern records centre. Retrieved 7 August 2018.
  11. "History of computing at the Met Office". Met Office website. Archived from the original on 9 December 2010. Retrieved 26 September 2010.
  12. Berry, F. J. (1 February 1959). AMOS - Ferranti Mark I*. "Intercode, a Simplified Coding Scheme for AMOS". The Computer Journal. 2 (2): 55–58. doi:10.1093/comjnl/2.2.55. ISSN 0010-4620.
  13. LEO Computers Society website
  14. Morgan, Tony (2012), THE DME LEO DME STORY (PDF)
  15. Holdsworth, David, LEO III software preservation
  16. Pelling, Nick (26 March 2002). "The Case For The First Business Computer". Retrieved 25 June 2013.

Further reading


  • Bird, P. J. (1994). LEO: The First Business Computer. Wokingham: Hasler Publishing Co. ISBN 0-9521651-0-4.
  • Caminer, D. T.; Aris, J. B.; Hermon, P. M.; Land, F. F. (1998). LEO: the incredible story of the world's first business computer. McGraw-Hill. ISBN 0-07-009501-9.
  • Campbell-Kelly, M., (1989). ICL: A Business and Technical History. Oxford: Clarendon Press.
  • Caminer, D. T., Aris, J. B. B., Hermon, P. M. R., Land, F. F. (1996). User-Driven Innovation: The World’s First Business Computer. London: McGraw-Hill. ISBN 0-07-009501-9.
  • Carmichael, H., editor (1996). An ICL Anthology, Chapter 6: LEO, Laidlaw Hicks, Surbiton, UK.
  • Ferry, Georgina (2003), A Computer Called LEO: Lyons Tea Shops and the World's First Office Computer, London: Fourth Estate, ISBN 1-84115-185-8
  • Hally, M. (2005). Electronic Brains: stories from the dawn of the computer age. Washington:Joseph Henry Press. Chapter 5: LEO the Lyons Computer. ISBN 0-309-09630-8.
  • Land, F. F., (1997). LEO, the First Business Computer: A Personal Experience. In Glass, R. L., editor. In the Beginning: Recollections of Software Pioneers, pages 134–153. IEEE Computer Society, Los Alamitos, CA.
  • PEP, (1957). Three Case Studies in Automation, PEP, London.
  • Simmons, J. R. M., (1962). LEO and the Managers, MacDonald, London.


  • Aris, J. B. B. (1996). "Systems Design — Then and Now". Resurrection, Summer issue 1996.
  • Land, F. F. (1996). "Systems Analysis for Business Applications". Resurrection, Summer issue 1996.
  • Aris, J. B. B. (2000). "Inventing Systems Engineering". IEEE Annals of the History of Computing, Vol. 22, No. 3, July–September, pp. 4–15
  • Land, F. F. (2000). "The First Business Computer: A Case Study in User-Driven Automation". IEEE Annals of the History of Computing, Vol. 22, No. 3, July–September, pp. 16–26.
  • Caminer, D. T. (1958), "...And How to Avoid Them". The Computer Journal, Vol. 1, No. 1.
  • Caminer, D. T. (1997). "LEO and its Applications: The Beginning of Business Computing". The Computer Journal, Vol. 40, No. 10.
  • Caminer, D. T. (2003). "Behind the Curtain at LEO: A Personal Reminiscence". IEEE Annals of the History of Computing, Vol. 25, No. 2, April–June, pp3–13.
  • Hendry, J. (1988). "The Teashop Computer Manufacturer: J. Lyons". Business History, Vol. 29, No. 8, pp. 73–102.
  • Land, Frank (1999). "A Historical Analysis of Implementing IS at J. Lyons." In Currie, W. G.; Galliers, R. D., editors. Rethinking Management Information Systems, pp. 310–325. Oxford University Press.
  • Savard, John J. G. (2018) [2005]. "Computer Arithmetic". quadibloc. The Early Days of Hexadecimal. Archived from the original on 16 July 2018. Retrieved 16 July 2018. (NB. Has information on the LEO III character set.)

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