Virtual machines

James P White
Thu, 22 May 1997 10:37:07 -0700

At 12:26 PM 5/22/97 -0400, Terrence W. Zellers wrote:
>On Thu, 22 May 1997, Dwight Hughes wrote:
>> | From: Terrence W. Zellers <>
>> |  
>> |    IMO it ***MUST*** be capable of fully virtualizing itself in 
>> | execution, not just emulation.   This means it must have a paging
>> | prefix algorithm, the ability to intercept any instructions which
>> Can this be done with an i486 or Pentium? Does it require special
>> hardware to pull it off properly?
>    The x86 architecture is NOT self virtualizable, no, but we're
>discussing an idealized VM to be emulated.  That can be done, of
>course, though at greater overhead than true on virtualizable hardware.
>A fair amount of the FREEVM discussion touched on that.

The x86 VM (386 and up) *is* self virtualizable using exactly the same
techniques as the IBM VM architecture (memory and i/o
mapping/paging/trapping, exception trapping and emulation, privilege

It is interesting to note that, AFAIK, no commercial OS for the x86 bothers
to support self virtual operation.  They all use it for security sandboxes.

James P. White                        Netscape DevEdge Champion for IFC
Director of Technology Adventure Online Gaming
Developers of Gameworld -- Live Action Role-Playing and Strategic Games        Pagesmiths' home is