Well, we'll see. I found _that_ one; process 1 managed to exec() init, do a fork(), and then the child process exec()'d the shell - then that apparently died, and the code in init falls through into: termall(); execl(init, minus, 0); when the single-user shell exits, so then init restarted; rinse, repeat. So a _lot_ of the code in mch.s seemed to be working correctly; system calls (2 exec()'s, and a fork()) worked, processing switching worked, device interrupts (for the disk and console tty) seemed to be working.. Not sure what's left! So I looked at mch.s again, to see what else _was_ there, and I noticed a place where I used R0 as a temp - with the MFPS/MTPS thing to get to the PS, instructions like: BIS #340, PS need to change to: MFPS R0 BIS #340, R0 MTPS R0 and R0 was being used to hold an arg (in pword:), and was being bashed. So I fixed it, and now the shell starts OK, but attempting to do any command (e.g. "echo foo"), things hang (the shell doesn't fork). If I type the interrupt character, the shell exits, and init restarts. Oh well, hopefully this one won't be too painful to work out. The system's mostly working, which I think will really help. Noel