[11] It used 828 dekatrons for volatile memory,[12] similar to RAM in a modern computer, and paper tape for input and program storage.

[11] The machine was decimal and initially had twenty eight-digit dekatron registers for internal storage, which was increased to 40 which appeared to be enough for nearly all calculations.

The design was noted for its reliability because in the period from May 1952 until February 1953 it averaged 80 hours per week running time.

Dr Jack Howlett, Director of the Computer Laboratory at AERE 1948–61, said it "could be left unattended for long periods; I think the record was over one Christmas-New Year holiday when it was all by itself, with miles of input data on punched tape to keep it happy, for at least ten days and was still ticking away when we came back.

Human mathematicians (a job role called a "hand-computer") could make calculations at a similar speed, but not continuously for the same lengths of time.

[1]In 1957, at the end of its life at Harwell, the Oxford Mathematical Institute ran a competition to award it to the college that could produce the best case for its future use.

[20][21] The museum, a registered charity, invited members of the public and industry to sponsor the restoration of the Harwell computer by purchasing one of 25 shares at £4,500 each.

[4] A 9 by 7 feet (2.7 m × 2.1 m) painting of the machine, Portrait of a Dead WITCH was made by the artist John Yeadon in 1983.