to that port. Although sending a message requires a system call, just as a request for system functionality on other systems requires a system call, under Mach sending the message is pretty much all the kernel does; handling the actual request would be up to some other program.

Thread and concurrency support benefited by message passing with IPC mechanisms because tasks now consist of multiple code threads that Mach could freeze and unfreeze during message handling. This permits the system to be distributed over multiple processors, either