The memory requirement is the sum of the memory the hosts needs plus what
you allocated for all vm's running concurrently plus a little overhead that
goes with running each vm. If Vista needs 1GB to run and you have 4GB
installed then allocating 256MB to an XP vm or 1GB to a Vista vm still
leaves you lots of memory to work with on the host. You allocate how much
memory a vm can use at the time you create the vm or change in the vm's
settings later. A vm does not use any memory when it is not running, of
course. VPC's New Virtual Machine wizard displays how much is available to
allocate at the time you are creating the vm. You would not be able to have
a vm use any memory that is not available to you as a user. A vm cannot use
memory that the BIOS has reserved for things like memory-mapped IO for your
devices, for example.

You allocate memory to a virtual machine just like you would select the ram
to install on a physical computer at the time you buy it.

It is appropriate to use VPC for running client operating systems and VS for
running server operating systems. And of course you can simply run both.

wrote in message $xE3.9@newsfe02.lga...
>I am trying to configure a computer (yet to be purchased) to use virtual
>(pc
> or server) and can't figure out how to plan for memory. If Vista is used
> as
> the host and it can only use a little more than 3gb of memory and if I
> understand my reading the sum of all memory for virtual machines could not
> exceed the physical memory available or is that the memory available to
> the
> host OS?
>
> If I have a 4gb machine can a VM use the part of that 4gb that my host
> Vista
> cannot use? What about on a 6gb machine?
>
> I need to support Vista, XP, Server2003 and Server2008 when available. The
> servers will have SQL2000, SQL2005 and SQL2008 (when available) and at
> times
> Oracle and PostgreSQL. The machine is for application development and will
> not be used in a "production" mode. It is not clear to me what is the best
> choice for my host OS. It seems that if I host with Server2003 I might be
> able to better utilize more memory, is that true?
>
> I am inclined to use Virtual Server, but don't really know if that
> provides
> any advantage over Virtual PC, any suggestions?
>
> Thanks

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