PSX ISO

PSX ISO, are these psp games? or ps1/2?

PS1. They can be run on a PSP with a custom firmware.

can all PS1 be playable in PSP?

Depends on the firmware.

Most PSX games play on PSP fine, some of the larger games tend to freeze up a little though. Diablo critical freezes on the second dungeon. Most FF games also freeze up, though there are fixes around for them.

PSX is an abbreviation for the Playstation 1. These roms are for PS1 emulators but a PSP with special custom firmware can be Soft-Modded to run these roms.