ISO 9660

The first standard used for data CDs on PC or IBM compatible computers. Unfortunately, in the beginning, many manufacturers had their own implementation of this loose standard. The ISO 9660 standard is constantly being upgraded and tightened to include new methods. The most important factor of this standard is when having both audio and data on one CD that the data is placed before the audio. This was originally referred to as High Sierra.
Apple Macintosh CDs use HFS, the same file system used with their other disk drives.
Also see: CD definitions, HFS, Hybrid, ISO, Joliet