Re: Winnt question

Eric Smith (
2 Nov 1996 04:10:48 -0000

> While we are on the subject of NT, does anyone know if the axp architecture
> can run as a virtual machine well enough to make running NT under a
> Linux/Alpha user process feasable?

I've been wondering exactly the same thing lately, and was on the verge of
posting the question to the list myself.

I don't know any reason why the base architecture can't be virtualized.

It seems to me that the problem will be PALcode. NT requires different
PALcode than Linux. If all PALcode instructions were priviledged, that
would be fine, because the VM would just simulate the NT PALcode. This
would only require minor changes to the Linux kernel. The VM manager
could actually run as a separate Linux process.

However, some of the PALcode instructions are not priviledged. I think
dealing with this would require modifying the SRM/Milo PALcode to allow
a means to trap PALcode calls from specific processes and bounce them to
the VM.

Although in principle the VM could fully simulate the raw iron to allow
unmodified NT HAL and device drivers to work, it seems like it might be
advantageous to write a special HAL and device drivers specifically for
the VM. This would be less general, but should be much easier and also
have higher performance. The NT DDK is necessary to write device drivers,
but it is readily available. I've no idea what is needed to write a new

Perhaps someone more knowlegeable about the Alpha architecture and
PALcode would care to comment?


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