CompuServe Messages

The CD-ROM XA spec. is 1) An extension to the CD-ROM specification. 2) An extension to the ISO 9660 specification, and 3) A specification for storing audio and video files. The CD-ROM XA specification was written long before Multisession ever existed. There is no direct relationship between Multisession and XA. The reason that they are so often mentioned together is PhotoCD. PhotoCD is the first popular application to use the CD-ROM XA sector format in the United States. PhotoCD is also the first popular application to use Multisession. Because of this, people think there is some connection between multisession an XA, when they are two entirely different things. A Multisession disc does not have to use XA format. It can use a standard CD-ROM format. A CD-ROM XA disc does not have to be multisession. It can be single session. A PhotoCD disc is always XA format, and can be single session or multisession. The CD-ROM XA spec is a proprietary Philips/Sony spec. They are the only source of a full XA specification. You can get some information on it from THE COMPACT DISC HANDBOOK by Ken Pohlman.