At Wed, 13 Jul 2011 09:17:55 +0100 (BST) CentOS mailing list centos@centos.org 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 _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos