Hi, I have an AMD 64 X2 4800+ processor (64bit), but I want to install a 32bit linux distro (Gentoo). However there are two types of initial binaries, x86 and i686. Now I think these refer to the instructions the CPU is capable, and as I have a cutting-edge CPU it supports everything (thats common), so which version, x86 or i686, has newer instruction sets, or is better suited to my processor.

Thanks in advance, Buck.

Probably i686. ix86 is sometimes a bulkier package because it supports 386,486,586, and 686. Since yours is newer, it should be 686.

I also found out from the "similar threads" at the bottom of the page. x86 is more backward compatable (which I don't need, so i686 for me)

The gentoo website has only x86 listed, not i686. Anyway, x86 refers to the architecture, i686 refers to the processor family. Architecture would be x86, alpha, SPARC, PPC, etc...subarchitecture would be i386, i486, pentium, pentium 2, pentium 3, duron, athlon, etc... x86 and i686 don't refer to the same piece of information. A backward compatible set (as the poster above put it) would be i386, not x86 (though if the program lists only the architecture then an x86 package could well be for i386, but it might be compiled for i686).

Also, a backward compatible binary wouldn't be any bulkier (as he puts it), it just means the code doesn't use optimisations designed for newer chips, such as MMX instructions, so it can run on anything 386 or better.

i'm not exactly sure so check the docs for your version of gcc it's all spelled out clearly in there
for that chip on a 32 bit system you should use
march=athlon-xp

if you use an older instruction set like say i686 from 20 years ago you waste your processor.