As a part of my need for studying 64 bit windows-machine architecture, read few things about 64 bit machines. The complexities comes when we are trying to run 32-bit applications (yes, we can run 32 bit applications on 64 bit machines.. Microsoft has given special emulator for this purpose..)
In a nutshell, 64 bit machines are having whole system for both 64 bit and 32 bit. e.g. you might find 64 bit version of regedit as well as 32 bit version of regedit in the 64 bit machine.
Another thing is, whenever we will start using native 64 bit applications, its going to boom the performance and we will jump a big leap towards high performance computing.
Want to read more benefit of 64 bit machines? Download document here