That may or may not be true; let me explain. The 11/23 is almost indistinguishable, in programming terms, from an 11/40. There is only one very minor difference (which UNIX would care about) that I know of - the 11/23 does not have a hardware switch register. Yes, UNIBUS devices can't be plugged into a QBUS, and vice versa, _but_ i) there a programming-compatible QBUS versions of many UNIBUS devices, and ii) there were UNIBUS-QBUS converters which actually allowed a QBUS processor to have UNIBUS peripherals. So I don't know which version of Unix was the first run on an 11/23 - but it could have been almost any. It is quite possible to run V6 on an 11/23, provided you make a very small number of very minor changes, to avoid use of the CSWR. I have done this, and run V6 on a simulated 11/23 (I have a short note explaining what one needs to do, if anyone is interested.) Admittedly, this is not the same as running it on a real 11/23, but I see no resons the latter would not be doable. I had started in on the work needed to get V6 running on a real 11/23, which was the (likely) need to load Unix into the machine over a serial line. WKT has done this for V7: http://www.tuhs.org/Archive/PDP-11/Tools/Tapes/Vtserver/ but it needs a little tweaking for V6; I was about to start in on that. As do a lot of us... :-) I'm not sure about that; I'd have to check into the Pro-350. If it has memory mapping, it should not be hard. Also, even if it doesn't have memory mapping, there was a Mini-Unix done for PDP-11's without memory mapping; I can dig up some URLs if you're interested. The feeling is, I gather, very similar. Having done that 'back in the day', I can assure you that it doesn't feel that different from the simulated experience (except that the latter are noticeably faster :-). In fact, even if/when I do have a real 11, I'll probably still mostly use the simulator, for a variety of reasons; e.g. the ability to edit source with a nice modern editor, etc, etc is just too nice to pass up! :-) Noel