I'm trying to come up with a way to automatically have the system compile the programs that need it with support for large files (> 2.0 GB). (I.E. Whoever compiles it does not HAVE to know it needs large file support.) On my V5R2M0 machine it seems to be enough to have a '#define __IFS64_IO__' in the code. (Per the manual) However, we develop on a V4R5M0 version machine to ensure compatibility with clients who are not up to date on their OS release. It appears that the above define does not work the same, and I MUST specify the SYSIFCOPT(*IFS64IO) option on the compile command. Does this sound about right? Is there something else I need to do on 4.5? Thanks!