Thursday, April 15, 1999 Published at 10:43 GMT 11:43 UK
Pioneers recall computer creation
Edsac: A working scientific tool
A major milestone in early computing will be celebrated in Cambridge, UK, this week.
The people who built the world's first fully operational and practical stored-program computer are meeting to celebrate the machine's 50th anniversary.
Edsac - Electronic Delay Storage Automatic Calculator - was a huge contraption that took up a room in what was the university's old Mathematical Laboratory.
It had 3,000 vacuum valves arranged on 12 racks and used tubes filled with mercury for memory. But despite its impressive size, Edsac could carry out just 650 instructions per second.
A program was fed into the machine via a sequence of holes punched into a paper tape. This generated pulses that the computer used to store the program and perform the desired calculation.
From day one, it operated as a complete system. Unlike earlier machines, none of the wiring or switches had to be altered to perform a new calculation.
"The machine wasn't retained by the engineers for experimental use," says Dr Peter Robinson from Cambridge's Computer Laboratory. "Very quickly, it entered general use for science around the university."
The world's first scientific paper to be published using computer calculations was done on Edsac - a genetics paper by R A Fisher.
Edsac 1 was replaced by Edsac 2 in 1958. Much later, the university turned to Titan, a commercial machine modified for university use.
Many of those who built and used Edsac are being brought back to Cambridge for a celebratory two-day seminar. They include Professor Maurice Wilkes who led the design team, and David Wheeler who wrote the very first program.
"Very little remains of the original machine," says Dr Robinson. "There is a chassis from the Edsac 1 and the paper tape reader that was used with it, and a thing called a mercury delay line which was the sort of memory used on that computer."
Sadly, hardly any of the original paper tapes survive.
"We've got some from later in the Lab's history but I've got a feeling most of them were used as streamers at children's parties," says Dr Robinson.
Edsac's vital statistics:
Pictures courtesy of the University of Cambridge Computer Laboratory.