Advanced SCSI Programming Interface
The Advanced SCSI Programming Interface (ASPI) is an established system of accessing drives (with its origins in 1970s mainframe technology) which today is commonly supported by CD-ROM reading/ripping software. The performance of some software/OS version combinations can be improved by installing the missing (or an alternative) ASPI driver, which is also sometimes called the ASPI 'Layer'.
Windows 2000 and XP come with ASPI pre-installed and software can come with its own version.
There is normally little to gain from changing ASPI unless prompted by a specific problem.
- Advanced SCSI Programming Interface on Wikipedia