The Motherboard Chipset

Most people think the microprocessor is the most important component of a computer. But modern processors do not directly control the computer's main memory or peripheral devices. They interface to them through a couple of special chips referred to simply as "the chipset". Because the chipset dictates the bus speed, type and amount of memory, and the type and number of I/O ports, much of a computer's performance is determined by its chipset.

The chipset traditionally consists of a "northbridge" chip, which controls high-speed interfaces like main memory and video display, and a "southbridge" chip which controls lower-speed devices like disc drives and bus expansion slots.

Lets explore a couple of common chipsets. The Intel 440BX chipset, the block diagram for which is shown below, consists of the 82443BX North Bridge, and the 82371EB PCI to ISA Bridge. It was designed to support the Pentium II and Pentium III processor.

Intel 440BX chipset

The 82443BX was designed for the Pentium II and Pentium III processor with a 100/133 MHZ Front Side Bus, it features support for one AGP (Accelerated Graphics Port), up to 1 GB of DRAM memory, and a 33 MHz PCI Bus. It interfaces to the 82371EB PCI to ISA Bridge.

The 82371EB (PIIX4E) PCI to ISA Bridge, in addition to providing an ISA bus, also provided a Dual-Channel Enhanced Integrated Device Electronics (IDE) Interface (Ultra DMA/33) which supports up to four IDE devices, 2 USB 1.0 ports, and support for a legacy keyboard and mouse.

Intel's MCH ICH Architecture

In 2000 Intel introduced a different architecture starting with the 820 which divides chipset functions between a Memory Controller Hub (MCH) chip and an I/O Controller Hub (ICH) chip.

Location of chipset

The picture above shows the location of the Intel 955X chipset, which consists of the 82955X MCH chip (covered by a cooling fan) and the Intel 82801GR ICH chip (covered by a cooling fan), on the Asus P5ND2 SLI motherboard.

Intel 955X chipset

The 82955X MCH supports up to 8 GB of dual-channel DDR2-667 memory, 1066MHz front side bus speed, and PCI Express architecture for up to 4GB/Sec of bi-directional bandwidth for graphics cards and other I/O devices.

The 82801GR ICH provides high definition audio, 10/100/1000 Network Connection, 4 SATA ports that allow for up to 3Gb/s of bandwidth for hard drives, RAID in 0, 1, 5, and 10 formats, and Native Command Queuing (NCQ) a technology designed to increase the performance of SATA hard disks.

There are hundreds, if not thousands of different chipsets. A chipset is designed to work with a specific microprocessor, or more properly, a family of chipsets is designed to work with a specific family of microprocessors. Similarly, a northbridge chip will only work with southbridge chips that its designed to work with.

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• Getting started with Raspberry Pi
• Introduction to Computer System Main Memory Operation
• Direct Memory Access (DMA)
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• Basic Computer Architecture
• The Computer's Chipset