"Rev 1" indicates a revision of the game disc's master code. In the late 1990s, Sony used incremental revision numbers on PlayStation CDs (often visible in the disc’s serial code, e.g., SLES-01376, with the revision indicated by a small mark near the inner ring or in mastering data). A Rev 1 suggests this disc was pressed after the original retail release (Rev 0) to address:
A lossless compression format designed to save storage space without losing any game data. It is widely used in emulators like DuckStation , RetroArch , and PCSX2 because it is significantly smaller than raw .bin or .iso files. Usage in Emulation metal gear solid spain disc 1 rev 1chd