This isn't a native port. The "RE4 PSP Better Compressed" is actually the of Resident Evil 4 repackaged and run through a specialized PSP emulator (usually a modified build of PSPRev or a prepackaged EBOOT.PBP). The "compression" isn’t just ZIP or CSO—it uses custom LZMA algorithms and strips dummy data from the original 4.5 GB PS2 ISO down to roughly 550 MB to 700 MB , small enough for a standard PSP Memory Stick Duo (or microSD adapter).
Here is a breakdown of what’s actually happening in those "highly compressed" download circles and how you can actually scratch that survival horror itch on your PSP. The Truth About "RE4 PSP" Files resident evil 4 psp highly compressed better
Genuine modern game files rarely compress below 100 MB without significant data loss, such as removing all audio and cutscenes. This isn't a native port
In PSP homebrew circles, “highly compressed” means: Here is a breakdown of what’s actually happening