Essential Folder Structure for PSP with Custom Firmware: /PSP, /ISO, /SEPLUGINS, etc.

Root of Memory Stick (or PSP Go internal) should contain:

/PSP
/GAME ← Homebrew EBOOT.PBP, signed plugins
/SAVEDATA ← Game saves (ULJS00000 etc.)
/SYSTEM ← CFW core (vsh.txt, flash0/, flash1/)
/THEME ← .ptf theme files
/MUSIC ← MP3/ATRAC/OGG
/VIDEO ← MP4/H.264 (368x208 max for 30fps)
/PHOTO ← JPEG
/COMMON ← PRX plugins (seplugins/)
/UPDATE ← Official firmware PUP (for recovery)
/ISO ← CSO/ISO game backups (for loaders like ISO Tool, Prometheus)
/SEPLUGINS ← plugin config (game.txt, vsh.txt, pops.txt)

Exact layout varies by CFW (PRO, ME, Infinity, HEN). Always back up /PSP/SYSTEM before modifying.