From: gerry77 at mail.com We obviously needed (and still need) the idle function because of power- consumption-related problems, so we were stuck and had to forget about that. OK, you tried playing nice -- so now play dirty! If you never found a way to make NULJOB (or whatever TOPS-10 has for an idle loop -- I've never been into the sources) identify itself to KLH10, why not hack up KLH10 to detect NULJOB itself? If you can't rebuild it then its address isn't going to change on you (on a given installation anyway). The *clever* part would be to do it w/o adding an address/mode test to every single opcode fetch (but even if you have to do that it'll still be fast enough). With E11 I got lucky -- one of the ways to display the null job blinky lights pattern on a PDP-11 is with the WAIT instruction, so all the OSes use it, and that's obviously the right time to take a snooze. Maybe there's something along those lines that KLH10 could use? John Wilson D Bit