Motherboard


A motherboard, also known as a mainboard, system board, logic board, and informally mobo, is the main printed circuit board in general-purpose computers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit and memory, and provides connectors for other peripherals.
Unlike a backplane, a motherboard usually contains significant sub-systems, such as the CPU, the chipset's input/output and memory controllers, interface connectors, and other components integrated for general use.

Nomenclature

Oxford English Dictionary traces the origin of the word motherboard to 1965, its earliest-found attestation occurring in the magazine Electronics. The term alludes to its importance and size compared to the components attached to it, being the "mother of all boards" in a computer system.
Several alternative terms for motherboard have been used in technical documentation and industry practice, including mainboard, system board, logic board, baseboard, and the informal mobo. These terms are functionally synonymous and reflect regional, corporate, or contextual preferences rather than a coordinated effort to adopt gender-neutral language.
System board was used by IBM in documentation for the IBM PC and its derivatives; however, higher-end models in the PS/2 line, such as the Model 80, used the term planar instead. Apple commonly uses logic board in its technical documentation for products such as the Apple II and the Mac. Intel typically uses baseboard in its technical manuals, though it also uses motherboard interchangeably. The term mobo is an informal truncation of motherboard, popularized by computer enthusiasts and builders in the 1990s.
The term mainboard sometimes describes a device with a single board and no additional expansions or capability, such as controlling boards in laser printers, television sets, washing machines, mobile phones, and other embedded systems with limited expansion abilities.

History

Before the advent of the microprocessor, the central processing unit of a computer was typically implemented using multiple printed circuit boards housed in a card cage, interconnected via a backplane—a board containing sockets into which the individual circuit boards were inserted. Early systems used discrete copper wiring between connector pins, but printed circuit boards quickly became the standard. The CPU, main memory, and peripheral components were each located on separate boards connected through the backplane.
With the rise of microprocessors, CPU functionality and supporting circuitry were consolidated onto a single board, while memory and peripherals remained on separate expansion cards plugged into the backplane. A prominent example is the S-100 bus, widely used in 1970s microcomputer systems such as the Altair 8800.
In the 1980s, popular personal computers like the Apple II and IBM Personal Computer featured publicly available schematic diagrams and technical documentation. This openness enabled rapid reverse engineering and the development of third-party motherboards. These clone and upgrade boards often provided enhanced performance or additional features, and were commonly used to modernize or replace original manufacturer hardware.
The first backplane to qualify as a motherboard was the Planar Breadboard, designed by IBM engineer Patty McHugh and used in the 1981 IBM Personal Computer.
During the late 1980s and early 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard. In the late 1980s, personal computer motherboards began to include single ICs capable of supporting a set of low-speed peripherals: PS/2 keyboard and mouse, floppy disk drive, serial ports, and parallel ports. By the late 1990s, many personal computer motherboards included consumer-grade embedded audio, video, storage, and networking functions without the need for any expansion cards at all; higher-end systems for 3D gaming and computer graphics typically retained only the graphics card as a separate component. Business PCs, workstations, and servers were more likely to need expansion cards, either for more robust functions, or for higher speeds; those systems often had fewer embedded components.
Laptop and notebook computers that were developed in the 1990s integrated the most common peripherals. This even included motherboards with no upgradeable components, a trend that would continue as smaller systems were introduced after the turn of the century. Memory, processors, network controllers, power source, and storage would be integrated into some systems.

Design

A motherboard provides the electrical connections by which the other components of the system communicate. Unlike a backplane, it also contains the central processing unit and hosts other subsystems and devices.
A typical desktop computer has its microprocessor, main memory, and other essential components connected to the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices may be attached to the motherboard as plug-in cards or via cables; in modern microcomputers, it is increasingly common to integrate some of these peripherals into the motherboard itself.
An important component of a motherboard is the microprocessor's supporting chipset, which provides the supporting interfaces between the CPU and the various buses and external components. This chipset determines, to an extent, the features and capabilities of the motherboard.
Modern motherboards include:
  • CPU sockets in which one or more microprocessors may be installed. In the case of CPUs in ball grid array packages, such as the VIA Nano and the Goldmont Plus, the CPU is directly soldered to the motherboard.
  • Memory slots into which the system's main memory is to be installed, typically in the form of DIMM modules containing DRAM chips. Can be DDR3, DDR4, DDR5, or onboard LPDDRx. Furthermore, some motherboards have dual memory slots which allows the installation of different memory types, such as either DDR2 or DDR3.
  • The chipset which forms an interface between the CPU, main memory, and peripheral buses
  • Non-volatile memory chips containing the system's firmware or BIOS
  • The clock generator which produces the system clock signal to synchronize the various components
  • Slots for expansion cards
  • Power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards., some graphics cards require more power than the motherboard can provide, and thus dedicated connectors have been introduced to attach them directly to the power supply.
  • Connectors for hard disk drives, optical disc drives, or solid-state drives, typically SATA and NVMe
Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as USB for mouse devices and keyboards. Early personal computers such as the Apple II and IBM PC include only this minimal peripheral support on the motherboard. Video interface hardware was also occasionally integrated into the motherboard; for example, on the Apple II. It was even less common on IBM-compatible computers, such as the IBM PCjr. Additional peripherals such as disk controllers and serial ports were provided as expansion cards.
Given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include heat sinks and mounting points for fans to dissipate excess heat.

Form factor

Motherboards are produced in a variety of sizes and shapes called form factors, some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible systems are designed to fit various case sizes., most desktop computer motherboards use the ATX standard form factor — even those found in Macintosh and Sun computers, which have not been built from commodity components. A case's motherboard and power supply unit form factor must all match, though some smaller form factor motherboards of the same family will fit larger cases. For example, an ATX case will usually accommodate a microATX motherboard. Laptop computers generally use highly integrated, miniaturized, and customized motherboards. This is one of the reasons that laptop computers are difficult to upgrade and expensive to repair. Often the failure of one laptop component requires the replacement of the entire motherboard, which is usually more expensive than a desktop motherboard.

CPU sockets

A CPU socket or slot is an electrical component that attaches to a printed circuit board and is designed to house a CPU. It is a special type of integrated circuit socket designed for very high pin counts. A CPU socket provides many functions, including a physical structure to support the CPU, support for a heat sink, facilitating replacement, and most importantly, forming an electrical interface both with the CPU and the PCB. CPU sockets on the motherboard can most often be found in most desktop and server computers, particularly those based on the Intel x86 architecture. A CPU socket type and the motherboard chipset must support the CPU series and speed.

Integrated peripherals

With the steadily declining costs and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard. By combining many functions on one PCB, the physical size and total cost of the system may be reduced; highly-integrated motherboards are thus especially popular in small form factor and budget computers. The integrated peripherals may also be called onboard devices.