Thanks.  Fair enough.  You mentioned PC/IX as /ISC's System III/ I'm not sure I ever ran ISC's System III port—only the V.3 port - which was the basis for their ATT, Intel, and IBM work and later sold directly. I'm fairly sure ISCalso called that port PC/IX, but they might have added something to say with 386 in the name—I've forgotten. [Heinz probably can clarify here]. Anyway, this is likely the source of my thinking. FWIW: The copy of PC/IX for the 386 (which I still have on a system I have not booted in ages) definitely has VPIX. ᐧ On Wed, Mar 13, 2024 at 11:28 AM Marc Rochkind &lt;mrochkind(a)gmail.com&gt; wrote: @Clem Cole <mailto:clemc@ccc.com>, I don't remember what it was. But, the XT had an 8088, so certainly no 386 technology was involved. Marc On Wed, Mar 13, 2024 at 8:38 AM Clem Cole &lt;clemc(a)ccc.com&gt; wrote: @Marc On Tue, Mar 12, 2024 at 1:18 PM Marc Rochkind &lt;mrochkind(a)gmail.com&gt; wrote: At a trade show, I bought a utility that allowed me to run PC-DOS under PC/IX. I'm sure it wasn't a virtual machine. Rather, it just swapped back and forth. (Guessing a bit there.) Hmm ... you sure it was not either VPIX or DOS/Merge -- ISC built VPIX in cooperation with the Phoenix Tech folks for PC/IX. I always bought a copy with it, but it may have been an option.   LCC did DOS/Merge originally as part of the AIX work for IBM and would become a core part of OS/2 Warp IIRC. Both Merge and VPIX had some rough edges but certainly worked fine for DOS 3.3 programs. The issue tended to be Win and DOS graphics-based programs/games that played fast and loose, bypassing the DOS OS interface and accessing the HW directly.  For instance, I never got the flight simulator (Air War over Germany) for Dad's WWII plane (P-47 Thunderbolt) to run under either (i.e., only under DOS directly on the HW. FWIW: In that mode, Dad said the simulator flew a lot like how he remembered it). Both Merge and VPIX used the 386 VM support and a bunch of work in the core OS.   Heinz would have to fill us in here. The version of the 386 port ISC delivered to AT&T and Intel only had the kernel changes to allow the VM support for VPIX to be linked in, but it was not there.   IICR (and I'm not sure I am) is that Merge could run on PC/IX also, but you had to replace a couple of kernel modules.  It certainly would work on the AT&T and Intel versions. ᐧ -- /My new email address is mrochkind(a)gmail.com/