If you're looking for a highly compressed PSP ISO file, I recommend checking out reputable websites that specialize in PSP game downloads, such as:
While many sites offer these files, these are frequently cited for having the most compressed versions: crash mind over mutant psp iso highly compressed top
A is a file that has been run through compression software (like WinRAR or 7Zip) using maximum settings. In some cases, modders have "ripped" unnecessary files (like update folders or foreign language audio) to shrink the size significantly—sometimes bringing the file down to 300MB - 500MB . If you're looking for a highly compressed PSP
If you have a full ISO and want to save space on your memory card: PSP ISO Compressor | Save Space on your Memory Card! crash mind over mutant psp iso highly compressed top