Power Mac G4

The Power Mac G4 debuted in late 1999 and was the first Macintosh to be dubbed a supercomputer, capable of doing more than a billion calculations per second. The computer was superseded by the Power Mac G5 and discontinued in the Summer of 2004.

Models

 * "Graphite" — The first "graphite" version came in two variants: an early "Yikes!" PCI-only logic board that was based on the pre-existing "blue & white" Power Mac G3, while a more advanced "Sawtooth" logic board introduced AGP graphics. Updates later added gigabit ethernet, digital audio, and Apple's new rewritable DVD "SuperDrive".
 * "Quicksilver" — This version upgraded specs and simplified the case design into a cleaner look.
 * "Mirror Drive Doors" ("MDD") — This version incorporated the DDR architecture of the Xserve, but heat and fan noise issues led it to being referred to as the "wind tunnel"

Export limitations
At the start and for about a year after the late 1999 debut, the Power Macintosh G4 was not available for the market in the mainland of the People's Republic of China, as the U.S. government deemed the "supercomputer" a "weapon". Mainland Chinese users, however, were able to get their hands on a Power Mac G4 after this limitation was removed. When the Titanium PowerBook G4 -- the first portable supercomputer -- was released, no similar sanctions were in place.