Why does 64-bit Windows need a separate "Program Files (x86)" folder?

Question

I know that on a 64-bit version of Windows the "Program Files" folder is for 64-bit programs and the "Program Files (x86)" folder is for 32-bit programs, but **why is this even necessary?**By "necessary", I don't mean "why could Microsoft not have made any other design decisions?" because of course they could have. Rather, I mean, "why, given the current design of 64-bit Windows, must 32-bit programs have a separate top-level folder from 64-bit programs?" Put another way, "what would go wrong if I somehow avoided the redirection mechanism and forced everything to install to the real `C:\\Program Files\\`?"There are plenty of questions on Super User and elsewhere that assert "one is for 32-bit programs, one is for 64-bit programs", but none that I can find give the reason. From my experience, it doesn't _seem_ to matter whether a 32-bit program is installed in the correct place or not.Does Windows somehow present itself differently to a program running out of "Program Files (x86)"? Is there a description that shows exactly what's different for a program installed in "Program Files (x86)" instead of "Program Files"? I think it's unlikely that Microsoft would introduce a new folder without a legitimate technical reason.

Answer 1

A direct way to answer this is to try it and see what breaks. Install a 64 bit program into the other 32 bit directory and try to run it. If it dose not break then the folder name dose not matter and it is just an organizational convince to help a user locate files and keep them separated. For instance a program with a 32 bit version and a 64 bit version with the same name. If it does break then it matters to windows what folder it gets the program from.

Answer 2

Whether a program uses 32 or 64 bit memory addressing has a very significant difference to the operating system. If the operating system doesn't know which addressing methodology is appropriate, the program simply won't work properly (if at all.) By segregating the program files into the two folders, that gives the operating system the information needed as to which methodology to use when executing a given app.