Messages in this thread |  | | Date | Fri, 6 Sep 1996 23:32:59 +0100 (BST) | From | Bryn Paul Arnold Jones <> | Subject | Re: [off-topic] Fully virtualisable CPUs |
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On Fri, 6 Sep 1996, Alan Cox wrote:
> > Sorry about being off-topic, but what makes a CPU fully virtualisable > > (that it can run several OSes in different VMs)? And what make the x86 > > not so? Is there any improvement in the latter x86 CPUs (Pentium, PPro) > > that makes virtualising easier? > > Not that off topic I think.. > > With all processors trying to do something that needs supervisor access > causes an exception. The difference with a processor you can virtualise is > that any instructions which allow you to query things like the supervisor > state and other supervisor mode instructions also causes a trap. That means > the underlying code (even a user mode program) can catch all of these traps > and the program it is managing thinks it is in supervisor mode when in > reality its in user mode but being 'helped' along. > > On the intel chips instructions that report the CPU state don't cause > an exception. Pity as if they did we could conceivably just boot windows95 > or nt or OS/2 or whatever in a window (and vice versa). > > Alan >
Hmm, that's not a very big difference (well it may be in silicon, but I don't think it's to big), they still could do that in the next round of P5/P6/P...'s ;).
Bryn -- PGP key pass phrase forgotten, \ Overload -- core meltdown sequence again :( and I don't care ;) | initiated. / This space is intentionally left | blank, apart from this text ;-) \____________________________________
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