Even when using a 64 bit version of Windows, the user can never really escape the past. For now, native 64 bit applications are rare, meaning that the majority of programs in use today are still 32 bit versions. In order to be able to execute these applications, Microsoft implemented the Windows-on-Windows 64 bit subsystem, also known as WoW64. In effect, WoW64 is an emulator for 32 bit applications which consists if the three DLL files WoW64.dll, WoW64win.dll and WoW64cpu.dll.

Because the applications are being run in an emulation environment, it is difficult to judge their performance objectively. Most apps runs slightly slower than in a native 32 bit system. Microsoft claims that especially memory-hungry software may even run faster. At any rate, our tests showed only marginal performance differences.

Another issue with 32 bit applications is the maximum memory chunk each process is able to address, namely 2 GB. This limit can be adjusted to 4 GB using with few special settings.

In the end, this means that even with 8 GB or more of system memory installed, each 32 bit application can only use a maximum of 4 GB. The only recourse these applications have is to page some of their routines that are currently not in use to the hard drive – which is obviously not going to improve performance.

The above screenshot shows that the files are loaded directly into RAM until 3 GB are reached. At this point, Photoshop is forced to write the files to the hard drive. As a result, CPU load also decreases, because the hard drive is much slower than system memory, meaning the CPU is waiting for data.

Native 64 bit applications are ready for the future, though, and each single process is able to address up to 8 Terabytes of memory. Nonetheless, developers will have to update their applications accordingly. Simply re-compiling the 32 bit applications with a 64 bit compiler is not sufficient, as this would result in each process still being limited to 2 GB.