"The layman when asked about the introduction of steam power will usually reel off Newcomen, Watt and Trevithick," said Chris Burton, of the Computer Conservation Society.
"But when it comes to computer pioneers they are absolutely baffled," he said. "They have no idea."
Conceived, designed and built by Tommy Flowers, Allen Coombs and Max Newman, the first Colossus was working in 1943 - three years ahead of the rival pioneering American machine known as Eniac.
For a long time the Electronic Numerical Integrator And Computer (Eniac) was better known than Colossus because the Official Secrets Act prevented those that worked on it talking publicly about their achievements.
Edsac ran its first programs in 1949 and was developed to act as the heart of a number crunching service for Cambridge scientists.
The creation of Edsac was backed by baking and catering giant J Lyons which bought a copy of the finished machine and turned it into the world's first business computer - the Lyons Electronic Office (Leo).
"It was the first programmable computer that went into routine operation," said science writer Georgina Ferry, author of a book about the genesis of Leo.
"What was innovative about Leo was not the hardware," she said, "but the systems and the way they used it."
John Pinkerton, David Caminer, Ernest Lenaerts, Derek Hemy and others at Lyons pioneered the use of computers in the dull repetitive tasks formerly carried out by legions of clerks. One of its first roles was to calculate how much each worker at the hundreds of Lyons tearooms was to be paid.