In September 2002, Apple announced that starting in January 2003, new Macintosh computers would only start up into Mac OS X, while retaining the ability to use most Mac OS 9 applications in Mac OS X's "Classic" environment.
These Macintosh computers only start up in Mac OS X:
PowerBook G4 (12-inch) and later models of 12-inch PowerBook G4 PowerBook G4 (15-inch FW 800) and later models of 15-inch PowerBook G4 PowerBook G4 (17-inch) and later models of 17-inch PowerBook G4 Power Mac G4 (FW 800) Power Mac G5 iBook G4 and iBook G4 (14-inch) and later models of iBook iMac G5 iMac (Flat Panel) with serial numbers of xx303xxxxxx or later iMac (17-inch 1 GHz) and later models of iMac eMac (ATI Graphics) most models (see Note) eMac (USB 2.0)
Note: For eMac (ATI Graphics) computers, startup in Mac OS 9 is available only with CD-ROM and some Combo drive configurations.