There is no official Resident Evil 4 release for the PlayStation Portable (PSP). Search results for "highly compressed ISO" often refer to unofficial fan-made mods or misleading files that may not work or could be malicious.
– Resident Evil 4 was never released for PlayStation Portable. Any “RE4 PSP ISO” you find online is either: There is no official Resident Evil 4 release
While there is no official release for the PlayStation Portable (PSP), the gaming community has created various modded versions or "ISO files" designed to run on the PPSSPP emulator . These are often highly compressed to roughly 200MB to 500MB for easier download and storage on mobile devices. Key Features of "Resident Evil 4 PSP ISO" Mods There is no official Resident Evil 4 release