CompuServe Messages

OK, here goes again. Broadly speaking, the XA spec. defines two sector types, Form 1 and Form 2. Form 2 sectors contain no error correction and are used for storing audio and video information in a file format defined by the XA spec. These audio/video files that are stored in Form 2 sectors using the XA audio/video format are commonly called XA streams. The XA spec. designates Form 1 sectors for storing any files that are not XA format audio/video files. Form 1 sectors do contain error correction. Pictures stored on a PhotoCD disc are stored in Form 1 sectors. PhotoCD picture files do not use the XA audio/video format. To read PhotoCD pictures, a CD-ROM drive only has to support Form 1 XA sectors. Most of the new PhotoCD compatible CD-ROM drives do only support Form 1 sectors. They do not support the Form 2 sectors used for storing XA audio/video ("XA streams"). Since there are currently many more drives that support MPC than support Form 2 XA, converting XA titles to MPC means those titles can run on many more CD-ROM drives. In theory, XA is a superiour technology. It is designed to run on many operating systems and should provide faster, smoother multimedia. However, MPC currently has a much larger installed base.