Originally Posted by Ejdaha
2. What does (64 bit) mean
The AMD64 and Intel EMT64 CPUs support two different (but related) instruction sets. In one, integer and address registers are 32 bits, in the other integer and address registers are 64 bits.
The most important difference is that 32 bit addresses support a 4Gb virtual space, part of which it reserved by the OS, so an individual task can only use about 3Gb of virtual memory. The addresses in 64-bit mode don't support a virtual address of the full 4G squared, but they do support more virtual address space than anyone could reasonably use.
If the OS is 64 bit, each program can be either 32 bit or 64 bit. But if the OS is 32 bit, even on a CPU with 64 bit support, all programs must be 32 bit.
Originally Posted by taxtropel
if you have an AMD 64 bit processor then you want to use a 64 bit linux (x86-64)
otherwise just an x86 flavor
I'm not sure of the pro and con factors to that choice. But most experts seem to advice differently than the above, saying:
If you have more than about 4Gb of physical ram, the PAE option that lets a 32-bit OS manage it is a bit messy so the 64 bit OS is a better choice.
If you need an individual program to take more than 3Gb of virtual memory (physical ram plus swap space) then you need the 64 bit OS.
If neither of the above is true, most expert advice I've seen says to use the 32 bit OS.