exec() was another problem - NT doesn’t support reusing a process for a new executable; exec() on Windows actually spawns a child process and then exits the par

exec() was another problem - NT doesn’t support reusing a process for a new executable; exec() on Windows actually spawns a child process and then exits the parent - which means exec() changes your PID. Both Cygwin and POSIX/Interix/SFU/SUA use the same workaround - maintain a separate Unix PID for each process. exec() changes the NT PID but leaves the Unix PID unchanged. So exec() creates a new process, but to Unix apps it looks like the same process. You are right that for many apps, rather than rely on emulated fork/exec, it was better to switch to native Windows facilities. Still, there was some value in being able to recompile Unix software with minimal changes (as Cygwin demonstrates). Even WSL now confirms that, albeit in a rather different way. Also, it was necessary to pass the POSIX test suite, which Microsoft briefly was concerned about (until they successfully lobbied the US government to drop POSIX certification as a procurement requirement).