Notes on the history of fork-and-join

As part of a PhD on code forking in open source software, Linus Nyman looked into the origins of how the practice came to be called forking. This search led back to the early history of the fork system call. Having not previously seen such a history published, this anecdote looks back at the birth of the fork system call to share what was learned, as remembered by its pioneers.
The fork call allows a process (or running program) to create new processes. The original is deemed the parent process and the newly created one its child. On multiprocessor systems, these processes can run concurrently in parallel. Since its birth 50 years ago, the fork has remained a central element of modern computing, both with regards to software development principles and, by extension, to hardware design, which increasingly accommodates parallelism in process execution.