On Mon, 05 Jan 2009 14:43:09 -0800, Darren New wrote:

> 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. :-)

It's also probably a bit more involved than XEN is.  I suppose I could 
ask my local XEN expert, was just recalling from a presentation he gave a 
few weeks ago at a conference I attended about how XEN actually works.  
It's pretty fascinating, OS or not.

> 
>> 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.

True.  I just wanted to make the point. ;-)

Jim

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