Thanks for your insight.
But nothing else in my Debian install uses up double memory.
Only XEN.
Why only XEN?
----- Original Message -----
From: "Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>
To: <xen-users@xxxxxxxxxxxxxxxxxxx>
Sent: Monday, February 05, 2007 3:28 PM
Subject: Re: [Xen-users] 32bit vs 64bit memory usage question
On 5 Feb 2007 at 10:00, Tom Miller wrote:
[...]
64 bit pointers and 64 bit memory address slots are twice as big as
corresponding 32 bit ones. So unless you have 4 GB of memory or more,
using 64bit software is actually slower for the system, not faster.
Are you sure? You are not saying that 64-bit programs are twice as large
as 32-bit
programs, do you? Besides of that I'd expect a 64-bit CPU to load a 64 bit
word
from memory in the same speed as a 32-bit CPU would load a 32-bit word.
Also these
AMD/Intel CPUs seem to have additional registers in 64bit mode.
I think the memory overhead comes from (As Andrew S Tanenbaum explained in
one of
his books about 10 years ago) the fact that the tables to manage the huge
64 bit
virtual address space are a great deal larger than those for 32-bit.
Finally (as in HP-UX 11), a 64 bit OS does not mean that every program is
a 64-bit
executable: a 32-bit Shell, Perl and Emacs is sufficient for most users
I'd think
;-)
Regards,
Ulrich
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