The Compiler directive P64 enables you to create a program that can be run on Server Enterprise Edition in 64-bit mode. If you do not use the P64 directive when you compile your program, the program can only be run on Server Enterprise Edition in 32-bit mode. Therefore, if you have developed an application on a 32-bit development system, you must recompile it with the P64 directive set, if you want to migrate it using Server Enterprise Edition in 64-bit mode.
The P64 directive is set by default if you check the 64-bit check box in the Build Settings dialog box.