Motherboard

A motherboard, also known as a mainboard, system board, logic board, and informally mobo (see "Nomenclature" section), is the main printed circuit board (PCB) 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 (CPU) 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. 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 (CPU) 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 (also called Super I/O chips) 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 (like the tablet computer and the netbook). 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:

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