On the old Sun gear if you sent a break signal over serial you wold interrupt the OS sure and be at the ROM monitor but you couldn't "resume" the OS, you could boot back up to single user or run level 3 but all of your previous state would be gone of course. Is that was you are referring to? I don't remember a disassembler being available from the prom monitor I do remember there a FORTH(sp?) interpreter though. Could you elaborate?