Originally Posted by mushroomboy
Any cpu that supports i686 can run all the binary prior. So i686 can run i386, i486, i586, ect... binary naturally. Since the linux kernel is built to i686 specifications (that or i386) the SB could naturally run the code with out any tweaks or modifications. CPU's don't so much have drivers or support, they have different types of language/code. To make it much easier we now call it x86 architecture, shortened and you can guess why. x*86 would be more correct, but not really needed.
x86_64 was the standard for 64bit set by AMD, mainly because it was better than what Intel created themselves (I think?). Their is the IA64, which IS NOT compatable with AMD cpu's. Though I think Intel tries to make all it's cpu's x86_64 friendly.
Short story, x86 designed cpu's can now run anything in the *86 family, whether it's i386 to i686. It will be this way for every x86 designed cpu.
intel's solution to 64 bit was to come out with a new architecture, you might have heard of the chip before, the itanium (it was a serious flop cause it didn't have backward compatibility with x86.)
i've come across a few of them in my day, not a whole lot work on them, even compiling from source is tedious, cause you have to modify the code here and there, and the distro choices for them are very "slim" and windows offering is even slimmer, i think the only windows install for them is nt4.0
they are great number crunchers, very fast in that aspect, i know guys who buy them slap a few together in a daisy chain, and then sell them to college kids to use as personal super computers.
and just a little technical nerd thing, x86_64 is sorta not a true 64 bit architecture, it can process 64 bit integers yeah, but its physical and virtue addressing space is only 48 bits, unless they extended to 52 bits like they were talking about, they also on this instruction set, extended the PAE feature from 36 bits to 52 bits (which pretty much gave it the same amount of addressable memory capabilities as it would running in 64bit "mode", so there is still some life left in the 32 bit x86