PS2 games only are playable only from internal dev_hdd0 and from CD/DVD (on B/C consoles - original & backup).
PS1 are playable from internal dev_hdd0, dev_usb*** (fat32), ntfs (external USB), from net_host (ps3netsrv), from CD (original & backup)
PSP are playable from internal dev_hdd0 and dev_usb*** (fat32).
PS3 are playable from internal dev_hdd0, dev_usb*** (fat32), ntfs (external USB), from net_host (ps3netsrv), from CD/DVD/Bluray (original & backup).
PS3 games can be in GAMES folder format (except ntfs) or ISO. All others must be ISO or cue/bin.
webMAN MOD can list PSP and PS2 stored on ntfs and net_host, but they are copied to internal HDD before play them.