Hard disk cabinets the size of washing machines and power demands that interfered with the London Underground tube network
A number of pieces published in the magazine about vintage computers sparked memories for three readers.
Peter Hickman read the letter from Terry Harvey about the ICT 1301 computer he helped build and realised he too had worked on the project in two stints. "I started in 1958, in the development lab at GEC's telephone works where I was a graduate apprentice, then later on Spon Street in Coventry where the computer was manufactured and tested.
"I still have some of its printouts along with the technical specification manual. The 1301 computer required a room that was at least 24ft by 24ft and a basic installation weighed nearly one-and-three-quarter tons," said Peter.
Henry Best recalls a school visit to the electronics engineering company, Ferranti. "When I was a schoolboy, my class was taken to visit Ferranti in Holborn, London, to see a computer. It was in a very large room that was reinforced with steel around the walls.
"The first thing that impressed me was the huge amount of punched paper lying around in rolls and reels. There was a teletype keyboard and a large green monitor. The monitor wasn't in front of the keyboard but high up on the operator's left.
"One of the operators asked us for a sum for the computer to do. He typed in 7x9 and then pressed the equals key. The awe we felt when the answer came up on the screen was tremendous. At the time, the most advanced technology we had used was a slide rule," says Henry.
"I remember the hard disk - although I don't think it was called that then - was a horizontal six-inch drum rotating at a leisurely speed and you could see the heads moving along its length. At about 4pm we were told they had to shut the machine down as it used so much electricity that it could disrupt the rush-hour London Underground service."
Henry found out later that the Ferranti computer was the direct descendant of University of Manchester's Baby computer.
The return of Ernie
Colin Porter helped reprogram a Leo III computer in 1970 for the change from eight to nine-digit Premium Bond serial numbers. The numbers were generated by one of the few vintage computers that was widely known about in its day: the Electronic Random Number Indicating Equipment, or ‘Ernie' for short.
"Its processing was complex and had to match names and addresses of winners with premium bond serial numbers. It then deleted those who had bonds repaid, bond numbers that had not been sold or were not eligible. All this and more was done via a string of large-diameter tapes in six-foot cabinets.
The Leo used A4-sized circuit boards and a Leo engineer was frequently on hand to replace any circuit board that malfunctioned, says Colin.
"We used punched card and tape for programming in a low-level language called Intercode, which required information to be input via numerical code. I remember that A was 41, J was 51 and S was 61. Directing the program to the start of a ‘sub-routine' was 80 and redirecting it back to the main program was 81.
There was little room for error where operators were concerned. "Inputs were done by keyboard operators, who I believe had to maintain 10,000 key depressions, with no more than one error, per hour.
The system was later upgraded to stacked Winchester-sized hard disks in cabinets the size of washing machines," says Colin.
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