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Block Diagram and Buses

The architecture of the main logic board is based on the PowerPC G3 microprocessor and three buses: the processor bus and two PCI buses, a primary 32-bit 66 MHz bus and a secondary 64-bit 33 MHz bus. The processor bus connects the microprocessor, cache, and main memory; the primary PCI bus is for an Apple graphics card solution; the secondary PCI bus connects the I/O devices. The I/O devices on the secondary PCI bus are

• Ultra DMA/33 (ATA-4) disk interface
• USB interface
• FireWire interface
• Paddington I/O controller IC
• PCI 33.33 MHz 64-bit slots B (2), C (3), and D (4)
• DEC/Intel 21154 PCI-PCI bridge IC

Figure 2-1 shows the main logic board block diagram.

Figure 2-1 Main logic board block diagram