PC Hardware in a Nutshell, 3rd Edition

Chipsets

Just as the motherboard defines a PC, the chipset defines a motherboard. The chipset determines the main characteristics of the motherboard—what processors it supports, what RAM types it can use, what bus types and speeds it supports, whether it supports standards such as AGP and USB, and so on. Chipsets are so named because they usually comprise two relatively large chips. Some chipsets contain three or more chips. A few chipsets, most of which are intended for low-cost systems, have all functions on one physical chip.

Figure 3-1 shows a block diagram for the 845PE, which until July 2003 was Intel’s flagship chipset for the Pentium 4 and Celeron processors. Block diagrams are helpful in understanding the functions of a chipset. Like most chipsets, the 845PE comprises a Northbridge chip, labeled GMCH, and a Southbridge chip, labeled ICH4. The Northbridge interfaces the CPU, memory, and AGP video—all of which are high-bandwidth components. The Southbridge can conveniently be thought of as a peripheral controller. The Southbridge manages low- and moderate-bandwidth components such as the PCI bus, IDE interface, USB 2.0 ports, and so on. Some motherboards supplement Southbridge functions by adding another chip, often called a Super I/O controller.

Figure 3-1. Block diagram of the Intel 845PE chipset (graphic courtesy of Intel Corporation)

Chipset makers often use one Southbridge ...