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From: pmaresch@hal.ulowell.edu (Pierre Mareschal)
Newsgroups: comp.os.mach
Subject: Mach as a Virtual Machine
Keywords: virtual machine - mach - design - architecture
Message-ID: <1991Apr16.133805.28465@ulowell.ulowell.edu>
Date: 16 Apr 91 13:38:05 GMT
Sender: Pierre Mareschal <pmaresch@ulowell.ulowell.edu>
Distribution: na
Organization: University of Lowell Computer Science, Lowell MA
Lines: 34
Originator: pmaresch@hal.ulowell.edu

Hi,

I am trying to answer this question:

			"Is Mach a virtual machine software?"

If one think of a virtual machine software as a "software copy of the
hardware" [1], the answer is no. Mach provides abstraction of hardware
and presents them at the user level, or operating system level.  On top
of Mach, all hardware looks or appears the same (right?).

If a virtual machine is defined as a "system in which the instructions
issued by a program may be different from those executed by the
hardware to perform a given task" [2].

On another hand, if one think of a virtual machine as a  piece of
software which allow to run different operating systems in it, the
answer can be yes.  Mach's designers claim Mach has, or offers the
possibility to implement several operating systems on top of it [3-4].

Does the answer depend on the definition of the virtual machine concept?

References:

[1] R. P. Goldberg: Architecture of virtual machine.
	Proc. of the Workshop on Virtual Computer Systems, Harvard U., 1972.
[2] R. P. Parmelee et al.: Virtual storage and virtual machine concepts.
	IBM System, Vol. 11, No. 2, 1972, pp. 99-130.
[3] R. F. Rashid: Threads of a new system.
	Unix Review, Vol. 4, August 1986, pp. 37-49.
[4] R. F. Rashid et al.: Mach: a foundation for system software.
	(can't remember where it was published...)
-- 
:- Pierre Mareschal <pmaresch@ulowell.ulowell.edu>