Historically, PSP ROMs have been distributed in two primary formats:
Originally designed for MAME (Multiple Arcade Machine Emulator) to compress CD-ROMs from the Sega CD and PlayStation 1, CHD has recently been adopted by PPSSPP (the leading PSP emulator) and modern handhelds like the Steam Deck and Anbernic devices. psp chd internet archive better
Here is why CHD is superior for PSP archiving: Keep the original dump and checksums as provenance evidence
The Archive allows torrent downloads. For large PSP CHD sets (50GB+), use the torrent option with a client like qBittorrent. Direct HTTP downloads will timeout on large folders. Historically, PSP ROMs have been distributed in two