Question

Here’s my scenario: the company I work has applications deployed to a 32bit Windows 2003 server and they want to move to a Windows 2008 Server that is 64 bit. It has been noted that these 32bit custom developed applications will not run on a 64 bit machine. I was not aware of this.

I have always thought that 32bit software CAN run on a 64 bit OS and just use the 32bit address. A 64 bit software on the other cannot run on a 32 bit OS. On a 64 bit, one does have to create 64 bit software but can and still also create software that is designed for 32 bit machines.

Can someone please elaborate on this?

Answer 1

In general, 32-bit applications will run under a 64-bit Windows (This is technically called WOW64 – Windows On Windows). This applies to all 64-bit Windows version to date, including Server.

WOW64 processes are marked in task manager with *32, For example: chrome.exe *32. Sysinternals’ Process Explorer has a separate column for this: Image Type (64 vs 32-bit).

If the app has components hosted inside other processes, then those components must accommodate processes they’re hosted in. Examples:

• Shell extensions are hosted in explorer.exe, whose bitness matches the OS’ bitness. Therefore, you should compile the extension in both 32- and 64-bit, and register the one matching the OS’ bitness during installation.
• Kernel-mode driver are hosted in the Kernel, whose bitness also matches the OS’ bitness. So, the above applies.
• Winsock LSPs (Layered Service Providers) are hosted in all processes, both 64-bit (native) and 32-bit (WOW64). Therefore, you should compile the LSP in both 32- and 64-bit, and register both in their respective catalogs during installation.

There are also considerations regarding file redirection (System32 / SysWOW64 / SysNative) and registry redirection (Wow6432Node), which I will not go into.