One anonymous uploader, active on Archive.org under the handle RetroRipper , explains:

In the golden age of handheld emulation, the Sony PlayStation Portable (PSP) remains a titan. With a library spanning over 1,300 titles—from Crisis Core: Final Fantasy VII to God of War: Chains of Olympus —the device (and its emulators, such as PPSSPP) is a nostalgia powerhouse. However, modern collectors face a brutal reality: A single UMD dump can range from 300 MB to 1.8 GB. When you multiply that by a full library, you are looking at over 1.2 TB of data.

Using high-quality CHD files as your baseline allows you to push emulators like to their absolute limits. Because the emulator doesn't waste CPU cycles struggling to read a poorly compressed CSO file, you can allocate your system resources toward maximizing visual fidelity.

To achieve the highest quality CHD (optimal for PPSSPP and future archival):

Download the desired PSP CHD files from the Internet Archive.

When users look for "extra quality" archives on the Internet Archive (archive.org), they are typically looking for specific curation standards: 1. True Lossless Redump Standards

The emergence of (Compressed Hunks of Data) as a top-tier format for PlayStation Portable (PSP) emulation has transformed how collectors archive and play their libraries. Traditionally, PSP users relied on CSO (Compressed ISO) or ISO files, but recent updates to the PPSSPP emulator (version 1.17 and newer) have introduced support for CHD, offering a superior balance of file size and performance. Why CHD is the New Standard