Three CDs for x86_64 compatible processors. You must use them on 64 bit x86 machines.
A dual architecture (i586 and x86_64) DVD. You can use it on both 32- and 64-bit x86 machines, the installer will detect your processor and boot the correct version of the installer. If you want to use a 32 bit installation on a 64 bit machine, you can select it by pressing F3 then F6 at the boot prompt.