The system board - also called the main board or the motherboard - is the main circuit board in a computer system and contains ways for interconnecting all other parts of a computer system. The system board contains all vital components of a computer, including the CPU, and provides the communication lines between all components. All possible connectivity is determined by the system board, as it determines everything that can be connected to a computer and how expandable it is.
The system board contains a series of electrical circuits running through it called buses that form a pathway of communication between components of a computer. The processor sits in a socket on the board and attaches a series of pins to allow for electrical current to pass. The board also contains connectors for power, memory, hard drives, CD and DVD-ROM drives, expansion cards, and every port contained on the back of a computer (i.e. where your mouse, keyboard, printer, etc. are connected), and other various components. This section will give a brief explanation of the most important parts of the system board.
There is a chip contained on the system board called the CMOS (composite metal oxide semiconductor). It contains a set of configuration and boot information called the BIOS (basic input output system). The BIOS controls all input and output that the computer performs, and tells the processor how to use every component that is attached to the computer. The BIOS is a piece of ROM (read-only memory) that has a small battery attached to it that allows it to retain changed settings whenever a computer is not plugged it. If the computer is unplugged and the battery is removed, the BIOS will lose all stored settings and revert to the defaults. It also contains configuration information that can be changed by a user to customize their computer-using experience, or for overclocking a computer. Some of the most important settings a BIOS controls are the time and date for a computer, hard drive and CD-ROM drive configurations, processor speeds, and memory speeds.
This is the part of the system board into which the computer processor, or CPU fits. The CPU performs all processing in the computer. The type of socket on the system board determines what type of CPU the computer is able to use. There are a large variety of sockets on the market today that utilize different socket types, and it is important to make sure that a processor is compatible with a specific system board.
Processor sockets consist of a series of holes into which metallic pins on the processor fit. The numbers of pins give the sockets their names (i.e. Socket 939). A lever on the socket will secure the processor by clamping onto these pins. The one exception to this rule is Intel’s newest line of processors which use Socket 775 in which the pins are contained on the system board, rather than the processor. Traditionally, when pins on the processor become bent or damaged, they will not fit into the socket. This means the pins either need to be repaired, or the processor needs to be replaced. Since modern processors cost so much more than modern system boards, it is much cheaper to replace pieces if the pins are contained on the board itself.
There are several types of processor sockets on the market today. The most modern ones are Sockets 478 and 775 for Intel CPUs, and Sockets 754 and 939 for AMD CPUs. AMD’s previous generation processors use Socket 462, which is most commonly referred to simply as Socket A.
The chipset refers to a chip or series of chips on a computer that determine the feature set of the system board. The type of chipset available will vary greatly on the manufacturer of the system board and type of processor the board uses. The chipset is a somewhat modern term, and is the combination of two older chips - the northbridge and the southbridge - in addition to any additional chips, such as RAID or SCSI. The northbridge chip is a microchip between the CPU and memory and determines what kind of memory is supported and at what speed and bandwidth. This will determine what memory chips will work in a given computer. The southbridge operates input and output operations of a computer and determines the type, number, and speed of all ports on a computer, such as printer ports, IDE ports for hard disk drives or optical devices (CD or DVD-ROM drives), and expansions slots. In modern chipsets, the north- and southbridge are typically one single microchip on a computer, and often use fans for adequate cooling.
A chipset will determine what features a computer has. USB ports, serial ATA for hard drives, onboard sound and network, and the number and type of expansion slots are all determined by the chipset. When shopping for computers, it is important to understand that the chipset will affect the capabilities of the system, as well as playing an enormous role in the cost of the system. Chipsets that offer less connectivity are often much cheaper, and cost should be considered. When shopping for the right system board, it is important to weigh what you want versus what you will use. The system boards with the best and most expensive features are often intended for high-end users which many devices to connect who require a lot of extra features. Also, value chipsets are targeted to users who need only the bare minimum number of connections, and are often slower and less efficient than the higher end equipment. When considering the purchase of a computer system, the feature set should be examined carefully to ensure that you get exactly what you'll need.
Form factor simply refers to the shape and configuration of a system board, and determines what type of power connector is uses and what cases it fits into. There are currently three form factors that are widely used: ATX, microATX, and BTX. ATX is the most common system board form factor used today, and most modern systems use this configuration. The illustration below is that of an ATX board.
MicroATX is very similar to ATX and uses the same power connector, but has much smaller dimensions. Because of this reduced size, microATX also has less room for expansion cards and ports, and is thus more limited. This form factor, also referred to oftentimes as small form factor (or SFF) is used primarily in home theater computers because of its small size. The layout is similar to the standard ATX form factor and will fit in any computer case that ATX fits into. However, ATX will not fit into microATX cases due to size limitations. Due to the smaller size of cases for microATX, cooling also becomes a factor, and it is necessary to make sure that any computer has good ventilation to prevent any possible damage to the system or its components.
BTX is a newer form factor with very few models on the market as of today, but it is gaining in popularity. While the power connectors are the same as ATX, the layout is much different. BTX system boards are built to optimize air flow through a case as components, such as the CPU or video card run hotter and hotter. A BTX case has a fan in the front of the computer blowing straight across the CPU and memory where the air is exhausted out another fan on the back of the computer. BTX is growing in popularity and will likely become the standard in the future, replacing ATX. Due to its altered layout, BTX is not compatible with ATX cases, though some cases can be configured (with some changing) to accommodate either type of board. BTX system boards will support every type of device and expansion card that can be used on an ATX board.
Expansion slots house expansion cards that add extra capability to a computer system. On standard system boards, these are located at the bottom left side of the board and are long slots that are white, brown, or black, depending on the type of slot. These slots allow a wide variety of expansion card to be placed into them to expand any number of features of a computer system, such as video or sound capabilities, adding network or modem support, adding additional connectivity ports, or adding special features. The possibilities for the slots are almost endless. Any card put into one of these slots is called a peripheral (though peripherals are not limited to just these).
Before using any expansion slots, it is first important to know the different types of expansion slots available. There is no compatibility between the different types of slots, and devices for one type will not fit correctly into any others. Forcing anything into the wrong slot can cause permanent damage to the expansion card, the system board, or both. There are three main types of expansion slots seen on most consumer-end computers today: PCI, AGP, and PCI Express.
The oldest modern slot and once that is used most. PCI stands for "peripheral component interconnection" and a computer can have a large number of these slots. There are a great deal of cards that will fit into these slots, and you can probably find any sort of card to fit your needs for PCI slots. Please note that these slots should not be confused with PCI-X slots - which are extended PCI slots common on mid-range business computers - or PCI Express (abbreviated PCIe). However, PCI-X cards are normally compatible in PCI slots, though at severely reduced speeds. PCI slots are the slowest of all the types of slots, and the total speed available is split amongst every PCI slot in the computer. This means that as you put more devices into different PCI slots, the total speed available to each one will drop. Most often, though, any reduction of speed is minimal and should not affect the use of these cards. Although the PCI slot is being replaced with the superior PCIe, it is still the most compatible slot with a large number of cards that can be used in it, and is around to stay for quite a while, still.
AGP stands for "advanced graphics port," and, as its name implies, is used for graphics cards (or video cards). A computer system is only able to have a single AGP slot, and these slots can only support video cards. AGP slots are superior to PCI slots for graphics, as they do not have to share speed and have dedicated small processors in order to help video output. In recent years, AGP has been the most widely used expansion slot for video, but it is quickly being replaced by the new and superior PCIe slot.
An upgrade to the old PCI interface, PCI express (PCIe) allows every slot to have its own speed and not share with other slots. PCIe slots come in several different sizes that represent the total bandwidth available to cards: PCIe x1, PCIe x4, PCIe x8, and PCIe x16. PCIe x1 slots are physically the smallest and the slowest of the slots, but are suitable for many cards. PCIe x4 is slightly longer and offer faster speeds. PCIe x16 is used primarily for video cards because of the high speeds it affords and is physically much longer than the other PCIe slots. With PCI express slots, cards made for any size slot can be used in any others, although using cards in larger slots will offer no performance increase, and placing cards in smaller slots will incur performance penalties. PCI express is quickly being adopted as the standard of slots, especially for video cards. However, many other types of expansion cards are slow at moving over to PCI express, and it may be awhile before the entire industry adopts this slot, though it is certain to happen.