The initial development of C occurred at AT&T Bell Labs between 1969 and 1973; according to Ritchie, the most creative period occurred in 1972. It was named "C" because many of its features were derived from an earlier language called "B," which according to Ken Thompson was a stripped down version of the BCPL programming language.
There are many legends as to the origin of C and the closely related Unix operating system, including these:
The development of Unix was the result of programmers' desire to play the Space Travel video-game. They had been playing it on their company's mainframe, but as it was underpowered and had to support about 100 users, Thompson and Ritchie found they did not have sufficient control over the spaceship to avoid collisions with the wandering space rocks. This led to the decision to port the game to an idle PDP-7 in the office. As this machine lacked an operating system, the two set out to develop one, based on several ideas from colleagues. Eventually it was decided to port the operating system to the office's PDP-11, but faced with the daunting task of translating a large body of custom-written assembly language code, the programmers began considering using a portable, high-level language so that the OS could be ported easily from one computer to another. They looked at using B, but it lacked functionality to take advantage of some of the PDP-11's advanced features. This led to the development of an early version of the C programming language.
The justification for obtaining the original computer to be used in developing the Unix operating system was to create a system to automate the filing of patents. The original version of the Unix system was developed in assembly language. Later, the entire operating system was rewritten in C, an unprecedented move at a time when nearly all operating systems were written in assembly.
By 1973, the C language had become powerful enough that most of the Unix kernel, originally written in PDP-11 assembly language, was rewritten in C. This was one of the first operating system kernels implemented in a language other than assembly. (Earlier instances include the Multics system (written in PL/I), and MCP (Master Control Program) for the Burroughs B5000 written in ALGOL in 1961.)
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