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Plasma Active Three releasedPlasma Active Three releasedPosted Oct 21, 2012 15:47 UTC (Sun) by raven667 (subscriber, #5198)In reply to: Plasma Active Three released by viro Parent article: Plasma Active Three released
Aside from os/2 I don't think the 286 was relevant except as a a faster 8086 and the 386 was the transition point. Dosbox shows that the vm route is viable.
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Plasma Active Three released Posted Oct 21, 2012 18:43 UTC (Sun) by nix (subscriber, #2304) [Link]
The VM route is viable *with modern hardware*, because its CPUs are much much faster and memory much more capacious than the systems being emulated. On late-1980s and early-1990s CPUs like the 80386 (which was introduced in 1985 and was becoming common in the early 1990s), it is wholly impractical to expect to be able to do instruction-level, let alone cycle-accurate, emulation of even an 8086, let alone a 286.
Plasma Active Three released Posted Oct 22, 2012 5:13 UTC (Mon) by raven667 (subscriber, #5198) [Link]
The 386 does run 8086 software just fine. Sure some runs too fast or whatever but the CPU has the appropriate guts to run 8086 software in a VM and that feature was in use at the time. For example Concurrent DOS 386.
Of course the rest of this is high speculation as it wasn't what happened.
Plasma Active Three released Posted Oct 22, 2012 15:21 UTC (Mon) by nix (subscriber, #2304) [Link]
I know it does. But if insn-level emulation was required, it couldn't possibly have (i.e. if it had done what dosbox et al do now).
Plasma Active Three released Posted Oct 22, 2012 17:12 UTC (Mon) by raven667 (subscriber, #5198) [Link]
Win3.1 with virtual memory enabled and WinNT, Win95 had the same problem so how they solved it should be sufficient. DOSBox does better but that may because it creates virtual video, sound and network devices in its VM. I don't think it does any more instruction emulation/trapping than a WinNT DOS window.
Plasma Active Three released Posted Oct 24, 2012 15:49 UTC (Wed) by nix (subscriber, #2304) [Link]
The two are quite different. Win3.1/NT/95 were all 32-bit systems, so they had the benefit of being able to use VM86 to do 90% of the work for them. In long mode (64-bit mode), vm86 no longer exists, so this approach cannot be used.
Plasma Active Three released Posted Oct 24, 2012 16:27 UTC (Wed) by raven667 (subscriber, #5198) [Link]
Thanks for the clear response, I hadn't thought about that. I'd forgotten about the differences between 32bit and 64bit mode on modern CPUs, and that dosemu and dosbox aren't the same thing.
Plasma Active Three released Posted Oct 21, 2012 19:07 UTC (Sun) by viro (subscriber, #7872) [Link]
Remind me, when had 386 boxen become widespread enough? IIRC, in the very late 80s... And overhead of vm86, while nowhere near that of hacks possible on 286, could still be heavy, depending on what the turd running in it had been doing. IRH the things had eventually gone that way, but it took a lot of time. IBM had invested too much into 286 boxen; OS/2 was only the software half of disaster...
AFAICS, there were two critical points in the making of that mess; one in mid-70s, when CP/M had been designed and spread, with resulting traditions of software that assumed it had essentially solitary control of bare hardware and another in the end of 70s, when internal politics in Intel has lead to 80286 design picked. Hell knows what happened in there - at the same time they had an even worse disaster going on (iAPX432) and chances of iAPX286 design to get accepted had to depend on how much could it be internally sold as aligned with iAPX432 one, but details are probably impossible to reconstruct by now.
Plasma Active Three released Posted Oct 22, 2012 5:17 UTC (Mon) by raven667 (subscriber, #5198) [Link]
In my speculative revised history I would think that the Xenix transition would happen in the early 90's, maybe with Win3.x and instead of developing new kernels for WinNT and Win9x. The result would probably have looked a lot like NeXT.
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