Re: [Xen-users] bare metal xen hypervisor

[Javier Guerra Giraldez <javier@xxxxxxxxxxx>]

On Tue, Mar 30, 2010 at 10:35 AM, balwant singh <bsingh21@xxxxxxxxx> wrote:
> also let me know if there is any baremetal xen hypervisor available as i
> read that i require one OS on which xen hypervisor will  be installed.

not exactly true.  the Xen hypervisor is as bare-metal as there is:
it's loaded by GRUB and takes over the whole machine before any other
kernel.

.... but....

it doesn't handle most of the hardware.  essentialy, it only manages
the CPU, RAM, and arbitrates access to PCI.  For everything else (hard
disks, network, USB, filesystems, etc) it relies on userlevel
processes running on Dom0

Dom0 is in fact as much a VM as any other one running on the machine;
the only differences are:

- it's started right after the Xen hypervisor, usually with parameters
given to Xen via GRUB
- by default Xen allows Dom0 total access to all PCI hardware
- it runs the Xen userlevel processes to provide hardware access to
Xen and DomU's

By delegating hardware access to Dom0, it avoids having to include
lots and lots of hardware drivers in the Xen source code.  As a
counter example, check the 'hardware compatibility' page of VMWare
most expensive options.  you'll see it supports a limited set of
network and SCSI cards.  Xen, on the other hand, support almost
everything that Linux supports.

-- 
Javier

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