[vox-tech] Apple & Linux

[Ken Bloom]

On Wednesday 10 January 2007 17:47, Matin Hashemi wrote:
> Hi Stuart
>
> Thanks for the detailed information..... I "thought" these virtual
> machines (Parallels, VMWare, etc) work a lot slower. A few years ago
> I used VMWare on my 800MHz AMD-based PC to write/run a few small
> programming class projects and it was like 20X slower than when I
> installed Fedora as a secondary OS. But I guess the world has changed
> a lot :-)
> http://en.wikipedia.org/wiki/Vanderpool
>
> I'm sure there is still some performance penalty. You said you are
> using those softwares; How much slower is it when you run some
> Win/Linux application in VMWare comparing to when you run it in a
> real Win/Linux OS? like 10%? it would be awesome then.....

"Virtual Machines" is a pretty big tent, and there's several kinds that 
operate in several different ways:
 * Application level, like the Java virtual machine, or the .NET virtual 
machine that contain one program.
 * System level, like Xen or VMWare

on another dimension:
 * Those that run programs written for the same kind of processor as the 
VM itself runs on, (running x86 programs on an x86 processor inside a 
guest OS). For example, VMWare
 * Those that run programs written for one processor on a different kind 
of processor (running PowerPC programs on x86, or m68k programs on 
PowerPC) For example, QEMU, Rosetta, and Apple's 68k emulator of yore, 
and those old version of Virtual PC that used to run on Macs.

It's the last kind that run very much slower than the processor they run 
on. VMWare has always been the a system-level VM for running a program 
on the same architecture as the virtual machine itself runs. That 
*should* be pretty fast. The processor itself can do all of the heavy 
lifting, and the virtual machine only has to catch various types of 
hardware accesses and emulate them.

There's one last thing that can bog things down greatly, and that's RAM. 
With two operating systems, you need to be sure they can both fit in 
RAM, otherwise things will start swapping and slow down a lot.

--Ken

-- 
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/
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