Re: [LAU] OT: 64 vs 32 bit?

On Mon, Sep 27, 2010 at 10:30:12PM +0200, Fritz Meissner wrote:
> On 27 September 2010 22:26, Josh Lawrence <hardbop200@email-addr-hidden> wrote:
> > Hi everyone,
> >
> > I'm late to the party when it comes to 64-bit machines, so apologies
> > in advance if I am asking something that should be obvious...
> >
> > I recently purchased a 64 bit machine and like it a lot, but I've
> > noticed that some software that is usually available on a 32 bit
> > machine isn't available in the 64 bit repos that I am using.  Can I
> > install the 32 bit version of my distro (Debian) on my 64 bit machine?
> >  I'm assuming that would give me access to all 32 bit software.  It
> > would also be a performance hit, correct?
> >
> Yes, you can install the 32 bit version. From what I have heard, the
> performance difference is not significant, but the major benefit of 64
> bit is being able to address more than 4 GB of memory, which is the
> limit of what a 32 bit OS can use.

One advantage to 64-bit machines is that there are more
CPU registers available in 64-bit mode, so some processing
goes faster, and more addressable memory.

That may be reason enough to run a 64-bit kernel while
keeping a 32-bit userland (libraries, applications, etc.)
Which some (including myself) do.

The advantage of 32-bit software is a smaller
memory footprint (e.g. 32 bits to represent an
integer instead of 64). There is a much wider software
availability, and fewer compatibility issues.

Although many say "64-bit is well established, no need
to worry about compatibility", I've had a few run ins.
At one point, I was maintaining two parallel Debian systems,
one 32-bit and one 64-bit, to track down such issues.

Some disadvantages to mixed systems, from the amd64 faq
at http://alioth.debian.org/docman/view.php/30192/21/debian-amd64-howto.html

    Q: I want to run i386 userland with a 64bit Linux kernel
    
    A: Running 32bit userland with a 64bit kernel is recommended
    only for servers needing the absolute stability of 10 years
    of 32bit debian, but without the memory limitations the IA32
    architecture bears, for example a 64bit mysql server on a
    system with 8GB or 16GB memory.
    
    Running the mixed setup on a workstation is not recommended,
    because iptables, the XFS filesystem, non-free NVidia and
    ATI binary drivers do currently not support it.
    
Iptables *does* appear to work for me in mixed environment,
at least the user interface part.

Cheers,

Joel
 
> Fritz

-- 
Joel Roth
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