History: The PowerMac G4 (AGP Graphics) was a major revision of the PowerMac line. Based on the Unified Motherboard Architecture, the G4 AGP was built around the PowerPC 7400 chip, which was dramatically faster than its predecessor, the PPC 750. The G4 AGP introduced a number of performance improvements, including AGP-based graphics, AirPort compatibility, a faster memory bus, DVD-ROM or RAM standard, an internal FireWire port, 2 separate USB buses for a combined 24 Mbs, a 2X (133 MHz) AGP slot, and up to 1.5 GB of RAM. Few 500MHz models actually shipped due to an "erratum" in the initial revision of the 7400 that effectively lowered the ceiling of the chip to 450MHz.