WITCH (computer)
Encyclopedia
The Harwell computer, later known as the Wolverhampton Instrument for Teaching Computing from Harwell (WITCH), or the Harwell Dekatron Computer, was an early British relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

-based computer. It is currently being restored at the National Museum of Computing
The National Museum of Computing
The National Museum of Computing is a museum in the United Kingdom dedicated to collecting and restoring historic computer systems. The museum is based at Bletchley Park in Buckinghamshire, England, and opened in 2007...

, where it is described as "the oldest original functioning electronic stored program computer in the world".

Construction and use at Harwell

The computer was built and used at the Atomic Energy Research Establishment
Atomic Energy Research Establishment
The Atomic Energy Research Establishment near Harwell, Oxfordshire, was the main centre for atomic energy research and development in the United Kingdom from the 1940s to the 1990s.-Founding:...

 in Harwell, Oxfordshire.
Construction started in 1949, and the machine became operational in April 1951. It was handed over to the computing group in May 1952 and remained in use until 1957.

It used dekatron
Dekatron
In electronics, a Dekatron is a gas-filled decade counting tube. Dekatrons were used in computers, calculators and other counting-related products during the 1950s and 1960s...

s for volatile memory
Volatile memory
Volatile memory, also known as volatile storage, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply...

, similar to RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...

 in a modern computer, and paper tape for input and program storage. Output was to either a Friden
Friden, Inc.
Friden Calculating Machine Company was an American manufacturer of typewriters and electronic calculators. It was founded by Carl Friden in San Leandro, California in 1934. Friden electromechanical calculators were robust and popular....

 teleprinter
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...

 or to a paper tape punch.
The machine was decimal and initially had twenty 8-digit dekatron registers for internal storage, which was increased to 40 which appeared to be enough for nearly all calculations. It was assembled from components more commonly found in a British telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

. Although it could on occasions act as a true stored-program computer, that was not its normal mode of operation. It had a multiplication time of between 5 and 10 seconds, very slow for an electronic computer.

As Cooke-Yarborough wrote of his design in 1953 "a slow computer can only justify its existence if it is capable of running for long periods unattended and the time spent performing useful computations is a large proportion of the total time available". 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
Jack Howlett
Jack Howlett was a British mathematician and computer scientist who was head of the Atlas Computer Laboratory for the duration of its existence.- Personal life and early career :...

, Directory of the Computer Laboratory at AERE
Atomic Energy Research Establishment
The Atomic Energy Research Establishment near Harwell, Oxfordshire, was the main centre for atomic energy research and development in the United Kingdom from the 1940s to the 1990s.-Founding:...

 1948–1961, 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." It was the machine's untiring durability, rather than its speed, that was its main feature. 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. Dr Howlett commented:

Subsequent use, renaming as the WITCH and disuse

In 1957, at the end of its life at Harwell, the Oxford Mathematical Institute
The Mathematical Institute, University of Oxford
The Mathematical Institute is the mathematics department at the University of Oxford, England. It forms one of the ten departments of the Mathematical, Physical and Life Sciences Divisional Board in the University....

 ran a competition to award it to the college that could produce the best case for its future use. The competition was the idea of John Hammersley
John Hammersley
John Michael Hammersley was a British mathematician best known for his foundational work in the theory of self-avoiding walks and percolation theory. He was born in Helensburgh in Dunbartonshire, and educated at Sedbergh School. He started reading mathematics at Emmanuel College, Cambridge but was...

, who had worked at AERE previously. The competition was won by the Wolverhampton and Staffordshire Technical College (which later became Wolverhampton University) where it was used to teach computing until 1973. The computer was renamed as the WITCH, the Wolverhampton Instrument for Teaching Computing from Harwell.

The WITCH was donated to the Museum of Science and Industry, Birmingham in 1973, where it was on display until the museum closed in 1997. The computer was disassembled and stored at the Birmingham City Council Museums Collection Centre.

Restoration

From September 2009, the machine was loaned to The National Museum of Computing
The National Museum of Computing
The National Museum of Computing is a museum in the United Kingdom dedicated to collecting and restoring historic computer systems. The museum is based at Bletchley Park in Buckinghamshire, England, and opened in 2007...

 at Bletchley Park
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...

, where began to be restored to working order as a Computer Conservation Society
Computer Conservation Society
The Computer Conservation Society is a British organization, founded in 1989. It is under the joint umbrella of the British Computer Society, the Science Museum in London, and the Museum of Science and Industry in Manchester. Many of the society's meetings are held at the Science Museum...

project. 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 £4500 each.

External links

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