Photos: The world's first business computer turns 60

Leo was a whale of a computer, weighing in tonnes and taking up some 5,000 square feet at Lyon's headquarters in Cadby Hall in Hammersmith, as seen here.

Not that Leo was especially large by the standards of the time. In 1951, computers were built using vacuum tubes or valves - glass tubes resembling light bulbs - that allowed them to process information. Almost 6,000 valves throbbed away inside Leo carrying out calculations, while 64 five-feet-long mercury tubes acted as its memory. Punched tape or card was used to feed data into Leo and to record its findings.

Leo was notoriously flaky at the start of its life - some 50 valves had to be replaced each week - but by 1953 Leo had proven to be so capable that Lyons gave it a new job: calculating the company's payroll.

By 1953, Leo was putting human mathematical calculators in the shade - able to calculate an employee's pay in less than two seconds compared to the eight minutes-plus it took a clerk.

Above, Lyons employees look at a circuit diagram during Leo I's construction.

Leo I proved so useful to Lyons that its successors, the Leo II and III, were sold to other organisations such as the post office and Ford motor company - introducing the world of business to the power of computing.

Pictured is a close-up of the control desk for the Leo I.

Despite its stature, Leo I's computing muscle couldn't begin to compete with the power of modern computers. Comparing processing speed alone, Leo I would be some 2,000 times slower than an iPad 2 and sucked up thousands of times more electricity.

Here is a shot of Leo I's decimal-sterling binary converter.

Lyon's technicians were inspired to build Leo by the Edsac - an early stored program computer that was built at the University of Cambridge in 1949.

Above is the printer-tabulator for the Leo I.