Today in 1949, the Electronic Delayed Storage Automatic Computer (EDSAC), the first practical stored-program computer, ran its first program and performed its first calculation. 

“… a thin ribbon of paper containing the program [to print a table of the squares of the integers] was loaded into the computer; half a minute later the teleprinter sprang to life and began to print 1, 4, 9, 16, 25…. The world’s first practical stored-program computer had come to life, and with it the dawn of the computer age,” Martin Campbell-Kelly and William Aspray recount the moment in Computer: A History of the Information Machine.

Maurice Wilkes, who was the head of the team that designed and assembled the EDSAC at the University Mathematical Laboratory at Cambridge University, wrote in his 1985  Memoirs about the origins of the EDSAC: “In the middle of May 1946 I had a visit from L. J. Comrie who was just back from a trip to the United States. He put in my hands a document written by J. von Neumann on behalf of the group at the Moore School and entitled ‘Draft Report on the EDVAC.’ Comrie… obligingly let me keep it until the next morning.  Now, I would have been able to take a xerox copy, but there were then no office copiers in existence so I sat up late into the night reading the report. In it, clearly laid out, were the principles on which the development of the modern digital computer was to be based: the stored program with the same store for numbers and instructions, the serial execution of instructions, and the use of binary switching circuits for computation and control. I recognized this at once as the real thing, and from that time on never had any doubt as to the way comptuer development would go.”

Wilkes went on to develop a practical “electronic calculating machine” (as he called the EDSAC in 1951) with a focus on speed of development and the use of proven technologies (even if they resulted in slower processing speed) that have been the hallmarks of successful engineering projects over the last sixty years. Say Campbell-Kelly and Apsray: “…the first two computers to be completed were both in England, at Manchester and Cambridge Universities. The reason was that none of the British projects had very much money.  This forced them to keep things simple and thus to avoid the engineering setbacks that beset the grander American projects.”

One consequence of the focus on what Wilkes called a “complete,” practical machine, was that the EDSAC became the first computer to be put to commercial use. Michael Williams, in A History of Computing Technology, tells us how the J. Lyons & Co., one of the sponsors of the EDSAC project, “produced a reengineered version of the EDSAC for their own use. They called the machine LEO, for Lyons Electronic Office… operational in the Fall of 1951. … Lyons used LEO I to derive the optimum mix for their brands of tea, to compute different kinds of tax tables, to process the payroll, and to assist in research  on crystallography. The speed of the machine can be suggested by the fact that a complete calculation of an employee’s wages and deductions would take about 1.5 seconds, as compared with a total of 8 minutes for the same job done by an experienced human clerk. LEO I remained in service with the J. Lyons & Co. for 14 years.”

A working replica of the EDSAC is being constructed at Bletchley Park, England.