64-bit Windows and 64-bit Computers

Since the release of Windows 7, the 64-bit computers get installed with a 64-bit Windows. 

A 64-bit computer with a 64-bit Windows can handle so much RAM memory as 192 GB. But a 32-bit computer with a 32-bit Windows installed can use a maximum of 3 to 4 GB (RAM) memory. Mostly around 3 GB because a large part of the address space is used by video cards and other devices such as network cards, sound cards etc. This is true even if you install 4 GB in the computer. Mostly only around 3 GB RAM will still be used.

Both 32-bit and 64-bit programs can be run on a 64-bit Windows. When a 32-bit program is run on a 64-bit Windows, a 32-bit emulator will be invoked to handle the 32-bit program.The emulator will make the 32-bit application to think it is running on a 32-bit Windows and the same functionality that is accessible on a 32-bit Windows will also be accessible for the program on the 64-bit Windows. Normally it will be hard for the program to know if it is running on a 32-bit or 64-bit system, but one sensitive phase is the installation of the 32-bit program. There exists special folders on the hard disk that is intended for 32-bit binary files only and it is very important that the installation program installs the 32-bit binary files to these folders. Some folders on the hard disk are intended for 32-bit binary files only and other folders are intended for 64-bit binary files only. If you place binary file with a specific bitness (32/64 bit) in a folder intended for another bitness the program will probably fail to work properly; in many cases the program will not even start.
 
Examples of binary files that is mentioned in this article are EXE files (program files), DLL files and OCX files (ActiveX components). Data files can usually placed in same folders and shared by both a 32 and 64 bit application.

Program Files folder and the Windows System folder

A 64-bit Windows has two different versions of the program files folder and the Windows system folder (system directory). One version is intended for 32-bit files and other version is intended for 64-bit files. The name of these folders, and the bitness they are intended for, is shown in the table below:
  

Below you can see the full path to the folders.

WOW64 is a shortening for ”Windows on Windows 64-bit” (can be read as "Windows 32-bit on Windows 64-bit"). It's a emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows. A compatibility layer is used as an interface between the 32-bit program and the 64-bit operating system.
 
x86 is the name of a processor architecture from Intel that handles 32 bit instruction sets. The x86 term have been used for a very long time and in the beginning it was used as a general term to refer to Intel 16/32 bit processors with names such 8086, 80186, 80286, 80386 etc. But since the release of the 80386 processor, the first real 32 bit processor, the term x86 have been used to refer to 32-bit processors that have an instruction set that is compatible with the old 80386 processor.

The 'System32' folder is for 64-bit files and the 'SysWOW64' folder is for 32-bit files

This can be somewhat confusing, but the System32 folder is intended for 64-bit files and the SysWOW64 folder is intended for 32-bit files. This may seem a bit illogical if you look at the folder names, but there is an explanation to this. It has to do with compatibility. Many developers have hard coded the path to the system folder in their applications source code. They have included "System32" in the folder path. And to preserve compatibility, if the application is converted to 64-bit code, the 64-bit system folder is still named System32.
 
But what about 32-bit applications that have the system path hard coded and is running in a 64-bit Windows? How can they find the new SysWOW64 folder without changes in the program code, you might think. The answer is that the emulator redirects calls to System32 folder to the SysWOW64 folder transparently so even if the folder is hard coded to the System32 folder (like C:\Windows\System32), the emulator will make sure that the SysWOW64 folder is used instead. So same source code, that contains a path with the System32 folder included, can be compiled to both 32-bit and 64-bit program code without any changes.

So remember:

• the SysWOW64 folder is intended for 32-bit files only
• the System32 folder is intended for 64-bit files only

It is very important that a binary file compiled to a specific bitness (32 or 64) is installed to the correct system folder. Otherwise the program that needs the file will not be able to load the file and will probably not work as expected.

The 'Program Files' and 'Program Files (x86)' folders
 
If you have a 64-bit Windows installed on your computer you have probably already noticed that there exist two folders for program files: the Program Files folder and the Program Files (x86) folder. The Program Files folder is intended for 64-bit programs and the Program Files (x86) folder is intended for 32-bit programs.
 
In many cases the program will start and run as expected even if you place the program in wrong folder, but if the program asks Windows for the path to the Program Files folder and want to access installed files in the folder, the wrong folder will be used and the program will likely fail to function. So to be sure that everything always works as expected, you should always install files with a specific bitness to the correct Program Files folder. So on a 64-bit computer with a 64-bit Windows, remember this:

• always install a 32-bit program into the Program Files (x86) folder
• always install a 64-bit program into the Program Files folder