It was with Windows Vista that Microsoft first made 64-bit operating systems easily available to regular consumers (while there was a 64-bit version of XP available, consumers didn’t have easy access to it, the way they do on Windows versions released ever since).
Certainly, Windows 64-bit is more efficient; what about the other difference?
Users who install 64-bit versions of Windows do know that there’s better performance to be had; 64-bit operating systems are able to use more than 3 GB of RAM, for instance, and are faster. To all appearances, though, 64-bit operating systems are identical to 32-bit ones; there’s just one prominent difference — when it comes to 64-bit installations, Windows places two different Program Files folders on the C: drive, rather than just the one seen on 32-bit installations. One is meant for 32-bit programs, and is called Program Files (x86) (x86 is the series of 32-bit Intel chips that always ran 32-bit Windows). The other, meant for 64-bit programs, is simply called Program Files.
Many users have been very curious about all of this — why does Windows need to separate its programs, and place them in two different folders? What happens if both 32-bit and 64-bit programs go into the same folder?
What would happen, for instance, if you were to install a 32-bit program on a 64-bit Windows installation, and deliberately tell the installer to choose the Program Files (x86) folder? Would something go wrong?
A separate folder isn’t strictly necessary
In most cases, installing a 32-bit application to the 64-bit folder wouldn’t make a difference. The Windows WOW64 system performs sophisticated tests to make sure that programs work correctly.
Problems can arise occasionally, though. When they are installed in the same folder, both 64-bit applications and 32-bit applications install their DLLs and executors in the same places. Since 32-bit applications are not programmed to know what to do when they encounter 64-bit DLLs, in theory, they could attempt to run 64-bit DLLs, and report errors.
Maintaining separate folders makes it easy for programmers, too
It’s important to remember that Windows isn’t just for end-users to use; it is also meant for the developers who build the programs that everyone uses. Working with incredibly complex masses of files and processes, programmers often get completely mixed up when files aren’t neatly put away in their own system folders. Separate folders are simply about staying organized.