"Highly compressed" versions (often found as .CSO files or repacks under 200MB-500MB) typically achieve their small size by stripping or modifying game data:

In this article, we’ll explore what highly compressed versions are, how they work, and what you need to know before downloading one. What is a Highly Compressed PSP Game?

Some extreme "RIP" versions removed background music or voice acting entirely, though this significantly degraded the emotional impact of Zack Fair’s story.

Just a quick heads-up:

A highly compressed version can reduce the file size from 1.6 GB to under 900 MB or even lower if certain assets are modified.

The original PSP version of Crisis Core: Final Fantasy VII typically has an uncompressed ISO file size of approximately . However, it can be highly compressed into the CSO (Compressed ISO)

To play a file, you will need: A PSP with Custom Firmware (CFW) or a PPSSPP Emulator. The .cso file. Steps for Emulators (PPSSPP): Download the Crisis Core CSO file. Move the file to your PSP/GAME folder on your device. Open PPSSPP, browse to the file, and click to play.