Can a 32bit process access more memory on a 64bit windows OS?

Newer versions of Visual Studio have a new flag which make 32-bit apps "big address space aware". Basically what it does is say that if it's loaded on a 64-bit version of windows, then it will get 4GB (the limit of 32-bit pointers). This is certainly better than the 2 or 3 GB you get on 32-bit versions of windows. See http://msdn.microsoft.com/en-us/library/aa366778.aspx:

Most notably it says:

Limits on memory and address space vary by platform, operating system, and by whether the IMAGE_FILE_LARGE_ADDRESS_AWARE value of the LOADED_IMAGE structure and 4-gigabyte tuning (4GT) are in use. IMAGE_FILE_LARGE_ADDRESS_AWARE is set or cleared by using the /LARGEADDRESSAWARE linker option.

Also see: http://msdn.microsoft.com/en-us/library/wz223b1z.aspx

Yes, under the right circumstances, a 32-bit process on Windows can access a full 4GB of memory, rather than the 2Gb it's normally limited to.

For this to work, you need the following:

• The app must be running on a 64-bit OS
• The app must be compiled with the /LARGEADDRESSAWARE flag.
• The app should be tested to make sure it actually works properly in this case. ;) (specifically, code that relies on all pointers pointing to addresses below the 2GB boundary will obviously not work here)