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

[Neil Pilgrim]

Phil Foxton wrote:
> On Thu, 2005-06-23 at 12:46 +0100, Dave Fisher wrote:
[...]
>>  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.

So are you saying that the EM64T intel chips don't allow running in 32- 
and 64-bits 'simultaneously'? I'm intrigued because I run some 32-bit 
apps here on my athlon64 running debian, in an i386 chroot (with i386 
debs), at the 'same' time as the rest of the system is running in 64-bit 
mode, ie. with the 64-bit debs. Are you saying that while the EM64T is a 
compatible arch to amd 64-bit, it can't do this?

> 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.

I thought the only software emulation required was if you run 32-bit on 
Itanium?

If I follow what you're saying, then I'm glad I didn't buy an EM64T chip!