"highly compressed" in the world of RPCS3 (the PS3 emulator) can mean two very different things depending on who you ask.

Example workflow for a 50GB game:

Before discussing compression, you must understand how RPCS3 reads games. Unlike emulators for cartridge-based systems (like SNES or GBA), RPCS3 does not magically “shrink” games. It expects data in one of two primary formats: