PaulDavisThe1st is saying that the Unix pattern of forking a process (and not calling exec) was an early form of multi-threading (or multi-processing), but unlike threads in NT and later pthreads, they didn't share memory and communication between them required some form of IPC.
Yep, absolutely corrrect. It was true at the lowest level (the semantics of fork) and it was true at the app/platform design level: in Windows you used threads inside a process, on Unix you used multiple communicating processes.
This obviously changed as pthreads came into being, and at this point, I suspect that the typical use for threads-sharing-memory and threads-not-sharing-memory is the same on most platforms.
A reminder that the task_t data structure describes threads and processes not just in Linux, but earlier Unixen also.
