Bill

To make 64-bit applications, click on the pull-down to the right of Win32 and select the Configuration Manager, choose <New>, x64, and select Yes on copy from Win32.

This does require having the 64-bit compiler installed.

You can build and run both 32-bit and 64-bit applications. (.lib, .DLLs come in 32-bit and 64-bit versions)

If everything is in FORTRAN you will likely have little problems. You may have problems where you expect some values to be 32-bit (e.g. HANDLE, pointers etc...)

Jim