A reduces the original 1.4 GB file down to roughly 300 MB to 500 MB . This compression uses lossless algorithms (CSO or ZSO) that remove dummy padding (empty data used to speed up UMD disc reads) and compress audio/video tracks.
Because this is a file, the emulator needs to work harder to decompress it. If you experience stuttering or audio crackling, try these fixes: Tomb Raider Underworld Psp Iso Highly Compressed
The "highly compressed PSP ISO" files found online are typically one of the following: A reduces the original 1