Unix Started Because Ken Thompson Wanted to Run a Space Game on a Cheaper Computer

In March 1969 Bell Labs pulled out of the Multics project — an ambitious time-sharing operating system being built jointly with MIT and General Electric. Multics had become slow and expensive, and Bell's management decided to stop funding it. Among the engineers left at loose ends was Ken Thompson, who had been part of the Multics team and who had also been quietly using a Multics test system to play a game he'd written called Space Travel. Each game ran the company about $75 in CPU time on the GE 635. After Multics was canceled, Thompson went looking for somewhere cheaper to run it.

He found a DEC PDP-7 sitting unused in the Visual and Acoustics Research department. While porting Space Travel onto the new machine, he started writing the surrounding pieces — a hierarchical filesystem, a small command interpreter, a few utilities — and discovered that what he was actually building was an operating system. With his wife and son away visiting his parents for a month, Thompson worked through it alone and emerged with a kernel, a shell, an editor, and an assembler. The team named it Unics, then Unix, partly as a one-user pun on Multics.

Dennis Ritchie joined in as the system spread to a PDP-11, and in 1973 the two rewrote it in C — a language Ritchie had built largely to make that rewrite tractable. The decision proved strategically enormous: an operating system written in a portable high-level language could be moved to other architectures, and Unix did so widely through the 1970s and 80s. Almost every modern operating system, including Linux, macOS, iOS, and Android, is descended from this PDP-7 hack.