In Windows NT, GDI functions send messages to the graphics subsystem rather than making direct function calls. To improve performance, functions that do not return a value, other than a return code, send the message asynchronously and immediately return TRUE. The requested action might subsequently fail, but the caller will not be informed of this. In OS/2, the graphics operations are performed during the GDI function call, so OS/2 validates the parameters and returns a useful return code. There are instances when OS/2 returns FALSE and Windows NT returns TRUE.