[Gllug] 64 bit v 32 bit

[Richard Jones]

On Sat, Oct 27, 2007 at 12:24:05PM +0100, Adrian McMenamin wrote:
> I have two desktops that are capable of running 64bit OSes though both
> are currently running 32 bit Ubuntu 7.10.
> 
> Is it worth upgrading - and will backing home directories on to tape,
> clean install of amd64 Ubuntu 7.10 and then restoring the home
> directories work for this? I did this last weekend for the other half
> when giving her a shiny new box so I know it will do the job for the
> same bit width...
> 
> Thoughts? Will I see any material difference in performance or is this
> just me indulging in my fascination for technology for no other reason?

Assuming you're talking about i386 vs x86-64, then yes (it's worth
upgrading) and yes (it'll continue to work).

The upside is that i386 is starved of visible registers, and x86-64
has many more available, and that is advantageous for compilers.  The
downside is that x86-64 programs are a bit bigger because all pointers
are 8 bytes instead of 4 bytes (the penalty is only around 10%[0] on
x86 because of the "compressed" instruction set[1]).  Overall 64 bit
is a win for many users.

The situation is different if you're running Linux on other platforms
like PowerPC or SPARC.  On these platforms the usual advice is to run
a 64 bit kernel with a 32 bit userspace.

Rich.

[0] http://macslash.org/comments.pl?sid=6356&cid=113229
[1] http://arstechnica.com/cpu/2q00/x86future/isa-future-1.html

-- 
Richard Jones
Red Hat
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