Robert Heller wrote: > At Wed, 13 Jul 2011 09:17:55 +0100 (BST) CentOS mailing list > <centos at 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. <snip> Coming in late, here, but 64 bit should run as fast or faster, since the registers are larger, and 64-bit hardware is optimized for by 64-bit compilers. In addition, you get twice as much data per fetch. The upshot is that there is no good reason for it to run slower. mark