On 2012-06-04 13:52, Brian Hechinger wrote: Anyone know how it works? I'd really like to get it working on Solaris. Simple. For a VAX, simh tries to detect the instruction sequence that the OS do in the idle loop. That's why it depends on which OS you are running on the emulated machine. For a PDP-11 it is (supposedly) simpler, since hopefully the idle loop of the OS uses the PDP-11 WAIT instruction, but that actually depends on which OS we're talking about. Not sure that RT-11 do, for instance. (I have some vague memory of discussing this with someone a few years ago, and coming to the realization that not all PDP-11 software might be using the WAIT.) For other hardware and OS combinations, the answers might differ even more. Johnny