Jim Henderson wrote:
> On Sun, 04 Jan 2009 10:10:29 -0800, Darren New wrote:
> 
>> Xen is an OS
> 
> I don't know that I'd agree with that.

Is VM/CMS an OS? I bet IBM would say so. :-)

> A hypervisor is a hardware 
> abstraction layer, messing about with the various memory rings in the 
> system in order to make the OS running within the hypervisor believe it's 
> running in Ring 0 when it's not in order to take advantage of memory 
> protection features in the hardware without tripping the native hardware 
> up when a child domain bombs out.

Sure. And Linux is a hardware abstraction layer, making your application 
think it has a linear RAM address space to mess with and providing linear 
sequences of bytes on disk to read and write (organized as a single tree of 
names), when none of those are actually true. One of the jobs of an OS is 
necessarily abstracting the hardware in *some* way, if you accept that 
maintaining state and managing resources between independent applications is 
part of the definition of an OS.

Of course you could argue either way.  I was more contrasting Xen against a 
BIOS than arguing that Xen must necessarily be considered an OS.

-- 
   Darren New, San Diego CA, USA (PST)
   Why is there a chainsaw in DOOM?
   There aren't any trees on Mars.

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