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SubjectRe: Linux + Win95 simultaneously


From:Pommnitz" <pommnitz@darmstadt.gmd.de>
Date: Mon, 03 Nov 1997 23:03:36 +0100
Subject: Re: Linux + Win95 simultaneously

>And just what RAM would
.....

Byron Davies wrote:
>> With a dual-processor Pentium, would it be possible in principle to
run
>> Linux and Win95 simultaneously, one on each processor?
......
>> the Mac. The same PCI board could be made to work by emulating
Windows I/O

This is where your theory breaks down. Key word here being emulate.


>> Supposing we have that working, now substitute a dual-processor
Pentium for
>> the two Pentiums linked by PCI, and substitute the memory bus for
the PCI
>> bus. Allocate different regions in memory for Windows and for
Linux, and
>> have the Windows drivers communicate through shared memory rather
than
>> through PCI.

What you've just described here is a windows emulator on Linux, such
as wine or softwindows. There is a very long technical explanation of
why that is, but here's the breviated version....AFAIK (so don't flame
me, I'm not perfect ;) )

The Intel MP spec, the paper that decribes what the intel SMP
architecture should be, says that memory and I/O have to be symetrical
in an SMP machine. There is no master processor. Both cpus access
whatever operating system is loaded from the boot sector of the disk
into lower memory ( I think its 0x10000 ? ). The machine begins by
assigning a Boot Strap Processor which is chosen by hardware or
through the BIOS. After BSP everything is divided into threads which
are scheduled for execution on a cpu symetrically. In order to
facilitate all of this, there has to be a controlling OS (accessed
through symetrical memory reads/writes) and you can then view the cpus
as drones. Whatever runs under the loader of the original OS would
have to be an emulation. The symetry of what goes on makes what you
are asking near impossible, and definitely impractical. Since all
memory is accessed symetrically and all I/O is done symetrically by
the APIC controllers, breaking the processors apart would undo all of
the work that went into the MP spec.

I think the question of WHAT RAM is a very good and valid one!
According to physics, two OSs can't occupy the same space at the same
time.

Besides, Linux and Windoze on the same machine at the same
time....it'd be like heaven and hell occupying the same space! ;)


raven
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