[Vm-dev] VM as a Xen guest

Guido Chari charig at gmail.com
Wed Dec 5 13:52:57 UTC 2012

Current status of SqueakNOS is that it runs correctly with old interpreter
VMs. We have a plan for making it compatible with new Stack and CogVMs.
That would mean performance boosts and also that new pharo and squeak
images that are really nicer that ones from some years ago will be
compatible. And also that updates on the image would be easily ported to


2012/12/3 Colin Putney <colin at wiresong.com>

> On Mon, Dec 3, 2012 at 10:15 AM, Javier Pimás <elpochodelagente at gmail.com>wrote:
>> I never quite understood how Xen compares to things like VMWare or
>> VirtualBox. Is it the same mechanism? What are the differences?
> Basically, Xen is a hardware abstraction layer. It takes care of
> communicating with devices and allocating resources to "domains". What it
> doesn't provide is virtual hardware. To run on top of Xen you write to an
> specific ABI, and make "hypercalls" which are analogous to applications
> making syscalls into an OS kernel. Some operating systems, (e.g., Linux)
> have been modified to be able to run in this mode, which is called
> "paravirtualization."
> VMware and VirtualBox and KVM on linux provide what is called HVM, with
> simulated hardware. The guest OS doesn't communicate with Xen via
> hypercalls, it thinks it's running on actual hardware, dealing with
> hardware interrupts etc.
> Paravirtualization is more efficient than HVM, but it requires special
> support from the guest OS.
> So if SqueakNOS can run on real hardware, it should work fine in HVM. It
> would probably need some work at the lower levels to support
> paravirtualization and run directly on Xen.
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