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 PS/2 Model 80|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:
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.

Peripheral card slots

A typical motherboard will have a different number of slots, depending on its standard and form factor.
Many motherboards feature two or more PCI Express 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 and AMD's 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 also feature PCIe x1 and possibly legacy PCI slots for other peripherals.
A standard, modern ATX motherboard will typically have two or three PCIe x16 slots for a graphics card, one or two legacy PCI slots for various expansion cards, and one or two PCIe x1 slots. A standard EATX motherboard will have two to four PCIe x16 slots for graphics cards, and a varying number of PCI and PCIe x1 slots. It can sometimes also have a PCIe x4 slot.
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, SATA-based M.2 SSDs, and wireless network interface controllers. M.2 provides a compact, high-speed interface that leverages the PCIe or SATA bus, depending on the configuration.

Temperature and reliability

Motherboards are generally air cooled, with heat sinks often mounted on larger chips in modern motherboards. Insufficient or improper cooling can cause damage to the internal components of the computer, or even cause it to crash. Passive cooling, or a single fan mounted on the power supply, was sufficient for many desktop computer CPUs until the late 1990s; since then, most have required CPU fans mounted on heat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional computer fans and integrated temperature sensors to detect motherboard and CPU temperatures and controllable fan connectors which the BIOS or operating system can use to regulate fan speed. Alternatively, computers can use a water cooling system instead of many fans.
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 capacitors on PC motherboards. 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 DC power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based electrolytes 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, 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.

Bootstrapping

Modern motherboards contain firmware stored in non-volatile memory such as ROM, EPROM, EEPROM, or NOR flash, which is responsible for initializing system hardware and loading an operating system from a boot device. The terms booting and bootstrapping derive from the metaphor "pulling oneself up by one's bootstraps", reflecting the self-starting nature of the process.

IBM-compatible personal computers (PC)

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 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, initialized hardware components, displayed system information, verified random-access memory, 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 —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 may include testing some of the following things:

SoCs and embedded systems

In RISC processor based embedded systems, the simpler boot firmware, such as Das U-Boot, may be used on the motherboard.