At Wed, 13 Jul 2011 09:17:55 +0100 (BST) CentOS mailing list <centos@xxxxxxxxxx> wrote:
>
> On Wed, 13 Jul 2011, John R Pierce wrote:
>
> > for many things, 32bit code is more compact and runs faster than 64bit
> > code (primarily because the code is smaller, so it requires fewer
> > fetches, more code fits in the cache, etc). 64 bit OS's totally
> > compatible with 32bit applications. of course, if a process needs more
> > than a couple gigabytes of address space, then 64bit is a no-brainer,
> > but there's really not that many applications which need that sort of
> > memory.
>
> Is that generally true? I thought running in 64bit got you access to twice as
> many registers and that generally you'd expect better performance from x86_64
> code not worse. While pointers would be doubled in size, most of your memory
> consumption would boil down to base types that'd be of the same size.
For some applications the performance advantage of having more
registers is small and the overhead of a larger executable is larger.
There is not any sort of absolute or fixed rule that says that all
applications *always* run faster, etc. when compiled for 64-bit,
although most do. Also there are odd-ball applications that it is not
worth the effort to make them 64-bit clean. And there are *still* a
few bits and pieces that have not (officially) migrated to 64-bit
(Adobe's Flash is not *officially* available as a 64-bit plugin,
although a 'beta' 64-bit version is available).
>
> jh
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