On Windows, depending on the bit-ness of an installed program, it will go to
Program Files or
Program Files (x86).
Additionally, many installation programs give you the option to install "For all users" to
Program Files (x86) or "For current user only" to
Users/<username>/AppData/<Local|Roaming>. You can make this decision based on privileges or preference.
But there is no convention for organizing user-specific programs by bit-ness. Why is that?