A motherboard is the central printed circuit board in most modern computers and holds many of the vital components of the system as well as provides connectors for other peripherals.
Before the microprocessor was introduced, computers were usually made in a card-cage case or mainframe with the gears connected by a backplane that consisted of a set of slots connected with wires. In much older designs the wires were discrete connections between card connector pins, but printed circuit boards soon became the typical practice. The CPU memory and peripherals were accommodated on individual printed circuit boards which plugged into the backplane.
Throughout the late 20th century, increasing the number of peripheral functions onto the motherboard became popular and more cost efficient. Motherboards also started to incorporate single ICs that were capable of sustaining a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. By the late 1990s, most personal computer motherboards supported an entire array of audio, video, storage, and networking functions without needing expansion cards.
The majority of computer motherboards made today are designed for computers that are IBM-compatible, which account for about 90% of global PC sales. Like a backplane, a motherboard supplies the electrical connections that allow the other components of the system to communicate; however, unlike a backplane, a motherboard also connects the central processing unit and houses other subsystems and devices.
A standard desktop computer contains a microprocessor, main memory, and other essential components, all of which are connected to the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices can be attached to the motherboard as plug-in cards or through cables. It is most common to integrate some of these peripherals into the motherboard itself. Another important component of a motherboard is the microprocessor’s supporting chipset, which supplies the supporting interfaces between the CPU and the various buses and external components. This chipset influences the features and capabilities of the entire motherboard. Modern motherboards include sockets; slots for the main memory and expansion cards to be installed in; a chipset that forms an interface between the CPU’s front-side bus, main memory, and peripheral buses; non-volatile memory chips including the system’s firmware or BIOS; a clock generator that creates the system clock signal to synchronize the numerous components; and power connectors that receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards. Furthermore, almost all motherboards include logic and connectors to support commonly used input devices as well as heat sinks and mounting points for fans to dissipate excess heat. Integrated peripherals are important parts of the motherboard, and with the progressively declining cost and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard itself.
Today’s motherboards will have a different number of connections depending on its standard. A standard ATX motherboard will normally have one PCI-E 16x connection for a graphics card, two conventional PCI slots for several expansion cards, and one PCI-E 1x. A standard EATX motherboard will have one PCI-E 16x connection for a graphics card, and many PCI and PCI-E 1x slots. However, nearly all motherboards come with at least four USB ports that have at least 2 internal connections on the board for wiring additional front ports and Ethernet. Some motherboards often have their sound and graphics chips built into the motherboard rather than needing a separate card.
Cooling motherboards is very important in maintaining their durability and reliability. Motherboards are usually cooled with heat sinks on larger chips. If it is not cooled properly, the computer is subject to crash. Newer motherboards have integrated temperature sensors to sense motherboard and CPU temperatures, and controllable fan connectors that the operating system uses to regulate fan speed.
Motherboards are manufactured in many different sizes and shapes, referred to as computer form factor. Some are specific to individual computer manufacturer, while others such as the IBM-compatible commodity computer have been standardized to fit various case sizes. Laptop computers commonly use highly integrated, miniaturized and customized motherboards. Motherboards also contain some non-volatile memory to initialize the system and load an operating system from an external peripheral device. Most modern motherboard designs use a BIOS to boot the motherboard. By doing so, the memory, circuitry, and peripherals are tested and configured.