There is. The C compiler on MiniUnix emits SOB instructions. The -11/05 doesn't implement SOB; however, the instruction emulator in MiniUnix (emul.s) is prepared to emulate it. (So MiniUnix should work fine on real -11/05's.) However, when set to an -11/05, Ersatz-11 treats SOBs as NOPs; they fall through without any effect. Without a trap, they can't be emulated either. This caused the problem with namei() failing (namei() calls bcopy(), which has a SOB in it), and probably caused the problem I was seeing with the C compiler, but I'm too burned out to check right now. Tomorrow. Noel