The 82371FB (PIIX) and 82371SB (PIIX3) PCI ISA IDE Xcelerators are multi-function PCI devices implementing a PCI-to-ISA bridge function and an PCI IDE function. In addition, the PIIX3 implements a Universal Serial Bus host/hub function. As a PCI-to-ISA bridge, the PIIX/PIIX3 integrates many common I/O functions found in ISA-based PC systems--a seven-channel DMA controller, two 82C59 interrupt controllers, an 8254 timer/counter, and power management support. In addition to compatible transfers, each DMA channel supports type F transfers. Chip select decoding is provided for BIOS, real time clock, and keyboard controller. Edge/Level interrupts and interrupt steering are supported for PCI plug and play compatibility. The PIIX/PIIX3 supports two IDE connectors for up to four IDE devices providing an interface for IDE hard disks and CD ROMs. The PIIX/PIIX3 provides motherboard plug and play compatibility. PIIX implements two steerable DMA channels (including type F transfers) and up to two steerable interrupt lines. PIIX3 implements one steerable interrupt line. The interrupt lines can be routed to any of the available ISA interrupts. Both PIIX/PIIX3 implement a programmable chip select. PIIX3 contains a Universal Serial Bus (USB) Host Controller that is UHCI compatible. The Host Controller's root hub has two programmable USB ports. PIIX3 also provides support for an external IOAPIC. This document describes the PIIX3 Component. Unshaded areas describe the 82371FB PIIX. Shaded areas, like this one, describe the PIIX3 operations that differ from the 82371FB PIIX. INTEL CORPORATION 1996, 1997