[Wylug-discuss] Linux on Intel 64-Bit Xeon

[Phil Foxton]

On Thu, 2005-06-23 at 12:46 +0100, Dave Fisher wrote:
> On Thu, Jun 23, 2005 at 12:33:11PM +0100, Phil Foxton wrote:
> > On Thu, 2005-06-23 at 12:15 +0100, Dave Fisher wrote:
> > >    1. Which Intel 64-bit architecture is a 'Dual 64-Bit Xeon'?  
> > >    
> > EM64T
> > >    As I understand it, Intel has two 64-bit architectures (one that is
> > >    and one that isn't 32-bit compatible).  Am I right about this?
> > > 
> > Not that I am aware of, but it might be worth asking Dell if the box is
> > a EM64T arch. box. AFAIK (and I might be wrong so don't quote me) Intel
> > started down the route of 64 with a completely new design (Itanium) but
> > it was NOT backwardsly compatible with X86 so they ended up licensing
> > the X86_64 arch. from AMD.
> 
> Thanks Phil, bit I am still a bit confused.  
> 
>   1. Is EM64T Itanium or X86_64?
Not as far as I am aware, EM64T is the Xeon which _will_ run in 32 bit
mode (I have a system in Manchester ATM that is running SLES 8 32 bit
version because Oracle HTB will not run in 64 bit at this moment in
time!
> 
>   2.  Isn't AMD's X86_64 capable of running 32-bit x86 code, and
>   therefore "32-bit compatible"? Whereas there never was a 32-bit
>   version of Itanium, so it its "32-bit _in_compatible"? What have I
>   failed to grasp?
> 
Yes you are correct, but the box in question is a 64 bit Xeon (following
me so far?) which will run in 64 AND 32 bit mode BUT not at the same
time.  There are ways around this, one is to have the box dual boot (not
really an option with a server, I am sure you will agree), one is to use
virtualisation (Xen) to create a 32 bit virtual machine on the 64bit
server and OS to allow the 32 bits apps to run.

The major difference between AMD and Intel on this front is that AMd
will run 32 bit apps on a 64 bit processor using hardware coded
translations, whereas the Intel one needs software translation which
adds extra over head if needing to run 32 bit apps on these boxes,
however if you have an app that is compiled for 64bit there seems to be
very little difference between AMD and Intel.
> Dave
> 
Hope that helps and that I haven't just stuck the stick in the pond and
wiggled it around a bit!

Phil

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-- 
Phil Foxton <phil at thefoxtons.org.uk>