Blog Image

Pride Month: Christopher Strachey

British computer scientist Christopher Strachey was born in 1916 in Hampstead, London. He is mainly known for creating the CPL programming language and was a significant contributor to the development of the Ferranti Pegasus computer in the 1950s. He is also said to have made the first ever video game based on a game of draughts. Strachey was an ingenuitive pioneer and was part of a larger group of influential scientists belonging to the LGBTQ+ community. 

Early Life

Strachey was born into a well known family in England and went to school at King’s College in Cambridge. During his time at King’s College, he suffered a nervous breakdown in his final two terms. According to his sister, it was because he was struggling to come to terms with his homosexuality. There is no other explicit mention of Strachey’s homosexuality, except for his declarations in his last years, as he kept matters of his private life very close to his chest. 

Strachey finally graduated from King’s and then delved into radar research during the war, then became a school teacher. His computing career started in 1951 at the age of 35, when he began programming machines at the National Physical Laboratory and Manchester University. 

The First Video Game

In 1952, whilst teaching at Harrow School, Strachey wrote a program for the Pilot ACE computer to allow a user to play draughts against the computer.. This idea was inspired from an article he read, “A Theory of Chess and Noughts and Crosses,” by Donald Davies, that was featured in the June 1950 issue of Penguin Science News. He chose draughts as it was the middle ground between noughts and crosses, which was too simple, and chess, which was too complex for computers at the time. 

In the summer of 1951, however, when Strachey ran the game on the Pilot ACE, it fully exhausted the memory. 

Interaction with Turing

Later in 1951, Strachey worked alongside Alan Turing, who at the time was assistant director of the Manchester University Computing Machine Laboratory. He heard about the Ferranti Mark I computer that Turing had written the programmer’s handbook for. This computer was far more capable and Strachey asked him for a copy of the handbook. Strachey told Turing about his ideas for the draughts playing program and Turing was interested in how this would work and encouraged Strachey to develop his idea further, exploring how to make the machine simulate itself. Strachey transcribed his programming into the operation of codes for the Ferranti Mark I and the game of draughts played well, at a reasonable speed, without compromising the computer’s memory. 

After his interaction with Turing, Strachey got a letter from M.H.A Newman, the professor of pure mathematics at Manchester. Newman had complimented Strachey on the quality of his programs and said that once one became available, he would love to offer him a post in his laboratory. Before this could happen though, Strachey caught the attention of Lord Halsbury, the managing director of the National Research and Development Corporation (NRDC) and, in 1951, was offered a technical officer position, which he took. 

The Pegasus

In his first year at the NRDC he was loaned to the University of Toronto to help program calculations for the St. Lawrence Seaway Project. During his time here he visited many research laboratories and computer manufacturers in the US. He made detailed notes of the order codes and instructions for different computers. He was one of the first people in the UK to realise that this subject needed more than just a passing thought. 

In 1954, he set up several meetings with Ferranti, pitching for a new machine, the Ferranti Packaged-Circuit Computer (later known as the Pegasus). He was able to set up a small department to produce the programming system and he played a big part in its specification. This was a high point for programming in the UK and had a big influence on future developments. 

In 1959, Strachey resigned to work as a freelance director and consultant. He had a consultancy agreement with Ferranti to create and deliver a scientific autocode for the new ORION computer. To help him with this work, he employed Peter Landin as his full time employee. However, Landin only spent part of his time on the autocode. Strachey encouraged him to spend time on a theoretical study of programming languages. Strachey felt as though he was financing “the only work of its sort being carried out anywhere”, especially England. With Strachey’s help, Landin’s work was put into a classic paper, “The Mechanical Evaluation of Expressions”. 


In 1962, Strachey was invited by Maurice Wilkes to work full time in the Cambridge University Mathematical Laboratory. He participated in developing a new programming language and compiler for the Titan computer. This project was named the Cambridge Programming Language (CPL). Strachey worked alongside David W. Barron to create a proposal, and then they collaborated with the London University Computer Unit. With this collaboration, the name was changed to the “Combined Programming Language”. Because of Strachey’s involvement and ideas it is also nicknamed “Christopher’s Programming Language”. It was first described in a published paper in 1963. At this time it was being used on the Titan Computer in Cambridge and the Atlas Computer in London. 

Strachey was influential for the design of programming languages, logical design of computers and the development of denotational semantics. Computing in Britain has Strachey to thank for the programming theory he directly influenced.

  • Written by Mikita Maru, June 28 2022