Many 64 bit architectures have been proposed; however, the x86-64 (aka
AMD64) architecture has picked up a lot of speed since its initial
proposal a couple of years ago. Most 64bit CPUs today support it, so it
looks like a good candidate for 64bit recompilation. The x86-64
architecture offers many more registers and can potentially speed up
games by a significant amount. Up to now, Pcsx2 has largely been
ignoring the 64 bit arena because there have been massive compatibility
issues, the developers weren't sure if it was really worth it, and
adding a new bug-free and fast recompiler to the existing code base is a
very painful process. Anyone seriously suggesting this to a dev would
have been laughed out of the chat room. However, the upcoming 0.9.2
release is looking very stable and after doing some research, we have
decided to add support for x86-64 recompilation, both for 64bit versions
of Linux and Windows (yes, Linux support is returning).