[amluto]

Linux has worked pretty hard to optimize fork(). This doesn’t mean that fork() is a good idea.

Windows does not historically depend on fork(), so there was no native fork(), so Cygwin kludged it up.

[JdeBP]

Actually, there is a native fork. There had to be, as POSIX personality support was a part of the Windows NT 3.1 design. What there wasn't was a Win32 form of fork. The Native API for Windows NT allowed it quite straightforwardly.

[jkrejcha]

Iirc Cygwin used to use it but iirc they moved away from it because they said that it was pretty slow

Though actually iirc werfault uses NtCreateUserProcess() to clone processes when writing out crash dumps to this day