Re: [tlug] Xen advice, please: Wine is not Virtualization

["Stephen J. Turnbull" <stephen@example.com>]

burlingk@example.com writes:

 > Another really big issue on the virtualization Vs WINE front.
 > Win is not a virtualization tool.  Wine will ONLY run on x86 compatible
 > processors.

This is true.

 > Xen, VMware, are virtual machines.  They emulate everything from the
 > ground up.

This is not.  I think you're confusing this use of "virtual machine"
with the kind of virtual machine that Java runs on.  They're actually
rather different concepts.

Xen et al do not emulate the CPU at all.  Most of the time application
and guest OS code is running directly on the CPU; that's why Xen and
VMware give such good performance in their virtual machines.

What they do is to allow multiple OSes to simultaneously have the
illusion that they control the whole machine, just as a multitasking
OS does for a single process.  This is done by substituting virtual
device drivers that hook in to the virtual machine monitor (Xen or VM
proper).  The Linux (Windows, NetBSD, etc) kernel proper should work
unchanged.  This isn't quite true because of memory and interrupt
management and maybe some others that really require intimacy with
both the kernel's core resource allocation functions and the hardware.

VM (at least the versions I tried several years ago) took the approach
of defining a virtual machine, and then providing Linux and Windows
drivers for that mechine.  The VM monitor was therefore pretty big,
and tended to be resource-intensive itself.  IIRC, you had to run a
special VMware X server which was even worse than a normal XFree86 3.x
X.  :-)

Xen takes a somewhat different approach, which requires more effort to
administer (at least at this point in time) but is substantially more
efficient than the VMware approach.

I would guess that now that CPUs are starting to provide hardware
support for virtualization that Xen and VMware will converge
(generally toward Xen on the monitor side, hopefully toward VMware on
the flexibility and convenience of administration).