The computer of 1951 is restored and commissioned

Engineers at the National Museum of Computer Science in Buckinghamshire completed the restoration of a rare WITCH computer , also known as Harwell Dekatron. In the video under the cut, you can see the shooting of the BBC channel , where the punched tape of the 50s is loaded into the car and it really starts to execute the program.

A couple of facts about this computer:
Initial assembly date: 1949-1951, commissioned by the Atomic Energy Agency
Computer weight: 2500 kg
Size: 6 x 2 x 1 m
Power consumption: 1500 W
Logic elements: 480 relays, 26 high-speed relays, 7073 contacts , 199 lamps, 18 switches
Counter: 828 decatrons
Productivity: about 100 Hz
Data entry and recording of result: paper tape

The following photo was taken in 1951, after the computer was started.



WITCH is the oldest working digital computer in the world. Calculations in it occur in electronic form, in decatrons. Decatron is a discharge lamp with 10 indicator cathodes. The discharge passes to the adjacent indicator cathode through two service subcathodes after supplying a pair of overlapping pulses . After ten pairs of control pulses, the discharge describes a full circle.


Decatron

The amazing thing is that you can go to the lamp and see with your own eyes the calculations. All 828 decatrons of the WITCH computer are visible to the naked eye, you can see the intermediate results of program execution, especially since a decimal number system is used instead of binary.

It is also interesting that decatrons turned out to be extremely reliable components, like all other modules of this computer. At one time, Harwell Dekatron worked 80 hours a week without a single failure. Old-timers say that once he was left to work 10 days unattended for the New Year holidays.

Restoring a WITCH computer took as long as three years. Initially, museum staff could not assemble all the components that had been gathering dust in the warehouse for 15 years on their own. I had to attract the original designers of the machine, who worked on its assembly in 1949-1951. Some of them are now over 90.