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A motherboard, also called a mainboard, a system board, a logic board, and informally a 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 computer memory, and provides connectors for other .
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.
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 , television sets, , , and other with limited expansion abilities.
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.
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 Computer mouse, floppy disk drive, , and . By the late 1990s, many personal computer motherboards included consumer-grade embedded audio, video, storage, and networking functions without the need for any 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.
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 card display and sound card, 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:
Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as USB for computer mouse 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 and were provided as expansion cards.
Given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include and mounting points for computer fan to dissipate excess heat.
A standard, modern ATX motherboard will typically have two or three PCI-Express x16 connection for a graphics card, one or two legacy PCI slots for various expansion cards, and one or two PCI-E x1 (which has superseded conventional PCI). A standard EATX motherboard will have two to four PCI-E x16 connection for graphics cards, and a varying number of PCI and PCI-E x1 slots. It can sometimes also have a PCI-E x4 slot (although this will vary between brands and models).
Many motherboards feature two or more PCI Express (PCIe) x16 slots, enabling support for multiple graphics cards or connecting multiple monitors directly without requiring specialized hardware. Some high-end models support multi-GPU technologies such as Nvidia's Scalable Link Interface (SLI) and AMD's CrossFire (formerly ATI CrossFire), which allow two to four graphics cards to operate in parallel, improving performance in graphics-intensive applications like gaming and video editing. However, as modern games and APIs increasingly favor single powerful GPUs, and with both Nvidia and AMD having largely discontinued active support for these technologies, multi-GPU configurations are now less common.
Modern motherboards typically include one or more M.2 slots—some high-end models offer up to four. These slots support a variety of devices, including NVMe-based solid-state drives (SSDs), SATA-based M.2 SSDs, and wireless network interface controllers (such as Wi-Fi and Bluetooth modules). M.2 provides a compact, high-speed interface that leverages the PCIe or SATA bus, depending on the configuration.
Some small form factor computers and home theater PCs designed for quiet and energy-efficient operation boast fan-less designs. This typically requires the use of a low-power CPU, as well as a careful layout of the motherboard and other components to allow for heat sink placement.
A 2003 study found that some spurious computer crashes and general reliability issues, ranging from screen image distortions to I/O read/write errors, can be attributed not to software or peripheral hardware but to aging on PC motherboards. c't Magazine, vol. 21, pp. 216–221. 2003. Ultimately, this was shown to be the result of a faulty electrolyte formulation, an issue termed capacitor plague.
Modern motherboards use electrolytic capacitors to filter the direct current power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based slowly evaporate. This can lead to loss of capacitance and subsequent motherboard malfunctions due to voltage instabilities. While most capacitors are rated for 2000 hours of operation at , their expected design life roughly doubles for every below this. At a lifetime of 3 to 4 years can be expected. However, many manufacturers deliver substandard capacitors,Carey Holzman The healthy PC: preventive care and home remedies for your computer McGraw-Hill Professional, 2003 page 174 which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures around the CPU socket exacerbate this problem. With top blowers, the motherboard components can be kept under , effectively doubling the motherboard lifetime.
Mid-range and high-end motherboards, on the other hand, use solid capacitors exclusively. For every 10 °C less, their average lifespan is multiplied approximately by three, resulting in a 6-times higher lifetime expectancy at . These capacitors may be rated for 5000, 10000 or 12000 hours of operation at , extending the projected lifetime in comparison with standard solid capacitors.
In desktop PCs and notebook computers, the motherboard cooling and monitoring solutions are usually based on a super I/O chip or an embedded controller.
In early microcomputers like the Apple II and IBM Personal Computer, firmware was stored in socketed ROM chips on the motherboard. Upon power-up, the central processing unit (CPU) would load its program counter with the address of the boot ROM and begin executing instructions from it. These instructions performed a power-on self-test (POST), initialized hardware components, displayed system information, verified random-access memory (RAM), and attempted to locate and load an operating system from a bootable peripheral device. If no such device was found, the system would either execute built-in software from ROM—such as Cassette BASIC (commonly known as ROM BASIC)—or display an error message, depending on the model. For instance, both the Apple II and the original IBM PC would launch their built-in BASIC interpreter when no bootable disk was present.
The boot firmware in modern IBM PC compatible motherboard designs contains either a BIOS, as did the boot ROM on the original IBM PC, or UEFI. UEFI is a successor to BIOS that became popular after Microsoft began requiring it for a system to be certified to run Windows 8.
When the computer is powered on, the boot firmware tests and configures memory, circuitry, and peripherals. This Power-On Self Test (POST) may include testing some of the following things:
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