CentOS - Apr 2007 - 32-bit vs 64-bit CentOS on 64-bit hardware

I was asked this question today and frankly, I didn't know the answer.  
So I thought I'd post it here....

If you don't need to access greater than 4GB RAM, is there any benefit 
to running the 64-bit version of CentOS vs the 32-bit one?  That's 
assuming, of course, that the target machine utilizes a 64-bit capable 
processor.  I hadn't seen any noticeable difference, but I haven't done 
any benchmarking either.

On a desktop machine, the 32-bit version seems preferable since there 
are closed source creature comfort apps that are not yet available in 
64-bit land, correct?

Cheers,

On 4/16/07, chrism at imntv.com <chrism at imntv.com>
wrote:
> I was asked this question today and frankly, I didn't know the answer.
> So I thought I'd post it here....
>
> If you don't need to access greater than 4GB RAM, is there any benefit
> to running the 64-bit version of CentOS vs the 32-bit one?  That's
> assuming, of course, that the target machine utilizes a 64-bit capable
> processor.  I hadn't seen any noticeable difference, but I haven't
done
> any benchmarking either.
>
If you need to have processes larger than about 2GB you need to use 64
Bit versions of CentOS.
> On a desktop machine, the 32-bit version seems preferable since there
> are closed source creature comfort apps that are not yet available in
> 64-bit land, correct?
>
Correct. While there is multilib to try and eleviate the pain of
this.. I find it and the Debian chroot option both more painful than
they should be.


-- 
Stephen J Smoogen. -- CSIRT/Linux System Administrator
How far that little candle throws his beams! So shines a good deed
in a naughty world. = Shakespeare. "The Merchant of Venice"

chrism at imntv.com wrote:
> If you don't need to access greater than 4GB RAM, is there any benefit
> to running the 64-bit version of CentOS vs the 32-bit one?  That's
> assuming, of course, that the target machine utilizes a 64-bit capable
> processor.  I hadn't seen any noticeable difference, but I haven't
done
> any benchmarking either.
Using AMD chips, 64 bit mode is significantly faster than 32 bit mode (20 to
30 percent, depending on the code), due to the extra registers. I don't
think this is the case for Intel chips. We run all our 64 bit desktops in
64 bit mode, and it's not too hard to get closed source 32 bit apps
working.

There are also advantages for things like LVM+RAID+XFS, as I believe the
stack size is larger, so it's less likely to crash.

Also, consider that not all of 4GB of RAM can be used in 32 bit mode. The
kernel takes up a large chunk of 4GB (depending on kernel compilation
options), so this limits the amount accessed by a single process.

Jeremy

-- 
Jeremy Sanders <jss at ast.cam.ac.uk>  
http://www-xray.ast.cam.ac.uk/~jss/
X-Ray Group, Institute of Astronomy, University of Cambridge, UK.
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