The British LEO I (Lyons Electronic Office I) computer, delivered in 1951, and modeled closely on the Cambridge EDSAC, was the first computer in the world that was used for commercial business calculations.

The computer was received in November 1951 at J. Lyons & Co. Ltd., after the company had partly funded the development and construction of the pioneering EDSAC at Cambridge University. LEO I's clock speed was 500 kHz, with most instructions taking about 1500 ms to execute. The computer's speed was constrained by its paper tape I/O. Its ultrasonic delay line memory based on tanks of mercury, with 1K (1024) 35-bit words (i.e., 4¾ K bytes), was four times as large as EDSACs.

Lyons used LEO I initially for valuation jobs, but its role was extended to include payroll, inventory, and so on. One of LEO I 's early tasks was the elaboration of daily orders which were phoned in every afternoon by their shops and used to calculate the overnight production requirements. This, arguably, could be the first instance of a computerised call center. The LEO project were also pioneers in outsourcing – in 1956 they started doing the payroll calculations for Ford UK on the LEO I machine.

In 1954, with the decision to proceed with LEO II and interest from other commercial companies, Lyons formed LEO Computers Ltd. This then was taken over by English Electric and this led to the breaking up of the team that had inspired LEO computers. English Electric went on to build the LEO III amd LEO 326 models. These allowed concurrent running of application programmes through the Master programme operating system. Some were still in commercial use until 1981. LEO Computers Ltd eventually merged with others to become ICT, and eventually ICL.

External links

• LEO Computers Society http://www.leo-computers.org.uk/
  • Record of LEO II installations http://www.leo-computers.org.uk/leo2s.htm
  • Record of LEO III installations http://www.leo-computers.org.uk/leo3s.htm