You can use the Compress Object (CPROBJ) command to compress selected objects in order to save disk space on the system or you can use the Decompress Object (DCPOBJ) command to decompress objects that have been compressed.
The object types that are supported for compression and decompression are *PGM, *SRVPGM, *MODULE, *PNLGRP, *MENU (only UIM menus), and *FILE (only display files or print files). Database files are not allowed to be compressed. Customer objects, as well as i5/OS-supplied objects, may be compressed or decompressed. To see or retrieve the compression status of an object, use the Display Object Description (DSPOBJD) command (*FULL display), or the Retrieve Object Description (RTVOBJD) command.