On Sat, Sep 20, 2003 at 02:01:41PM +0100, Albert Schwar wrote:
> > Kris ... you hit it ...
> >
> > > As far as I understand VMWare, it is not an emulator, actually,
> > > but a type of hypervisor that uses many dirty tricks to provide a
> > > virtual PC on top of a host PC. ...
>
> Correct. It does not provide virtual machines.
> You are limited to the specified versions of specified OSes.
> May be useful if you want to run some backlevel stuff
> while migrating.
Actually, this is not entirely correct either, but it does point at a fairly
big limitation in VMWare (and x86 capability for being virtualized)... VMWare
actually can run more OSes (and versions of OSes) than those 'supported' by
VMWare. E.g. I had Plan9 running (in text mode, due to not having the specs
for the video card VMWare emulates) on VMWare years ago, and now Bell Labs has
is running with GUI. But it is not at all supported by VMWare, and VMWare does
not contain any code that is customized to make it possible.
The main issue is that VMWare's virtualization is not a perfect virtual copy
of the underlying hardware, but rather a close derivative. The Plex86 project
(now deceased) had a very good explanation on the issues involved with trying
to virtualize the x86 architecture.
In comparison to z/VM, the biggest limitation I see (functionality wise) is the
limited accessibility to underlying hardware resources. If VMWare would be able
to run as an OS on the hardware, while providing its guest instances with things
like assigning processor affinity, and accurate CPU utilization control, we'd
be in a much happier place :)
Granted, it is still a long stretch from z/VM, but when you're not really into
writing your own OS on the hardware, VMWare does the job pretty well. I've not
ran into any Linux/*BSD/Plan9 version I've tried that did not run well on VMWare
which makes it (for *my* purposes) a perfectly decent virtual platform to do OS
testing/development on. For running production servers on it, I'd be more
hesitant, because of the aforementioned limitations on how you can control the
host resources amongst multiple VMWare guest instances. I sincerely hope that
VMWare (perhaps with input from IBM, since they partnered) will put some work
into that realm.
Kris
PS: User Mode Linux is another one mentioned in this thread... It's definitely
something very different because it truly only provides you with a limited
user-level Linux instance rather than providing a virtual machine that you
can run an OS on.
--
Never underestimate a Mage with:
- the Intelligence to cast Magic Missile,
- the Constitution to survive the first hit, and
- the Dexterity to run fast enough to avoid being hit a second time.
