What is the difference between ASPI, ASAPI and Native drivers?

EAC communicates directly with the CD-ROM drives. For this EAC made use of several interfaces which do the low level work. You was able to choose the interface by your own in the EAC options (depending which interfaces are installed in your computer).

Nowadays, ASPI is not used anymore. In WinNT/2000/XP EAC is able to use a native interface in that OS.