PC Motherboard

The main circuit board of a microcomputer. The motherboard contains the connectors for attaching additional boards. Typically, the motherboard contains the CPU, BIOS, memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive. Collectively, all these chips that reside on the motherboard are known as the motherboard's chip set.

On most PCs, it is possible to add memory chips directly to the motherboard. You may also be able to upgrade to a faster PC by replacing the CPU chip. To add additional core features, you may need to replace the motherboard entirely.

Motherboard is sometimes abbreviated as mobo.

Sockets and CPUs

A Socket 939 motherboard

The CPU is the first thing that comes to mind when many people think about a computer's speed and performance. The faster the processor, the faster the computer can think. In the early days of PC computers, all processors had the same set of pins that would connect the CPU to the motherboard, called the Pin Grid Array (PGA). These pins fit into a socket layout called Socket 7. This meant that any processor would fit into any motherboard.

Today, however, CPU manufacturers Intel and AMD use a variety of PGAs, none of which fit into Socket 7. As microprocessors advance, they need more and more pins, both to handle new features and to provide more and more power to the chip.

Current socket arrangements are often named for the number of pins in the PGA. Commonly used sockets are:

• Socket 478 - for older Pentium and Celeron processors
• Socket 754 - for AMD Sempron and some AMD Athlon processors
• Socket 939 - for newer and faster AMD Athlon processors
• Socket AM2 - for the newest AMD Athlon processors
• Socket A - for older AMD Athlon processors

A Socket LGA755 motherboard

The newest Intel CPU does not have a PGA. It has an LGA, also known as Socket T. LGA stands for Land Grid Array. An LGA is different from a PGA in that the pins are actually part of the socket, not the CPU.

Anyone who already has a specific CPU in mind should select a motherboard based on that CPU. For example, if you want to use one of the new multi-core chips made by Intel or AMD, you will need to select a motherboard with the correct socket for those chips. CPUs simply will not fit into sockets that don't match their PGA.

Chipsets

The northbridge and southbridge

The chipset is the "glue" that connects the microprocessor to the rest of the motherboard and therefore to the rest of the computer. On a PC, it consists of two basic parts -- thenorthbridge and thesouthbridge. All of the various components of the computer communicate with the CPU through the chipset.

The northbridge connects directly to the processor via the front side bus (FSB). A memory controller is located on the northbridge, which gives the CPU fast access to thememory. The northbridge also connects to the AGP or PCI Express bus and to the memory itself.

The southbridge is slower than the northbridge, and information from the CPU has to go through the northbridge before reaching the southbridge. Other busses connect the southbridge to the PCI bus, the USB ports and the IDE or SATA hard disk connections.

Chipset selection and CPU selection go hand in hand, because manufacturers optimize chipsets to work with specific CPUs. The chipset is an integrated part of the motherboard, so it cannot be removed or upgraded. This means that not only must the motherboard's socket fit the CPU, the motherboard's chipset must work optimally with the CPU.