Single-board computer

Single-board computers (SBCs) are complete computers built on a single circuit board. The design is centered on a single or dual microprocessor with RAM, IO and all other features needed to be a functional computer on the one board. The first true single-board computer (see the May 1976 issue of Radio-Electronics) called the "dyna-micro" was based on the Intel C8080A, and also used Intel's first EPROM, the C1702A. The dyna-micro was re-branded by E&L Instruments of Derby, CT in 1976 as the "MMD-1" (Mini-Micro Designer 1) and was made famous as the example microcomputer in the very popular 8080 "BugBook" series of the time. SBCs also figured heavily in the early history of home computers, for example in the Acorn Electron and the BBC Micro. Other typical early single board computers were often shipped without enclosure, which had to be added by the owner, examples are the Ferguson Big Board and the Nascom.

With the development of PCs there was a sharp shift away from SBC, with computers being constructed from a motherboard, with functions like serial ports, disk drive controller and graphics being provided on daughterboards. The recent availability of advanced chip sets providing most of the I/O features as embedded components allows motherboard manufacturers to offer motherboards with I/O traditionally provided by daughterboards. Most PC motherboards now offer on-board support for disk drives including IDE and SATA with RAID, graphics, Ethernet, and traditional I/O such as serial and parallel ports, USB, and keyboard/mouse support. Plug-in cards are now more commonly high performance graphics cards (really graphic co-processors), high end RAID controllers, and specialized I/O cards such as data acquisition and DSP (Digital Signal Processor) boards.

Applications

Chassis Plans S6483 Single Board Computer Major Components

Single Board Computers are now commonly defined across two distinct architectures; no slots and slot support.

Embedded Single Board Computers are boards providing all the required I/O with no provision for plug-in cards. Applications are typically gaming (slot machines, video poker), kiosk, and machine control. Embedded Single Board Computers are much smaller than ATX motherboards, and provide an I/O mix more targeted to an industrial application such as on-board digital and analog I/O, on-board bootable flash so no hard drive is required, no on-board video, etc.

The term "Single Board Computer" now generally applies to an architecture where the Single Board Computer is plugged into a backplane to provide for I/O cards. In the case of PC104, the bus is not a backplane in the traditional sense but is a series of pin connectors allowing I/O boards to be stacked.

Single board computers are most commonly used in industrial situations where they are used in rackmount format for process control or embedded within other devices to provide control and interfacing. Because of the very high levels of integration, reduced component counts and reduced connector counts, SBCs are often smaller, lighter, more power efficient and more reliable than comparable multi-board computers.

The primary advantage of ATX motherboards versus Single Board Computers is cost. Motherboards are manufactured by the millions for the consumer and office markets allowing tremendous economies of scale. Single Board Computers, on the other hand, are in a specialized market niche and are manufactured in much smaller numbers with the resultant higher cost. Motherboards and Single Board Computers now offer similar levels of feature integration meaning that a motherboard failure in either standard will require equivalent replacement.

The primary advantage of a PICMG Single Board Computer is the availability of backplanes offering virtually any slot configuration including legacy ISA support. Motherboards tend to the latest slot technology such that PCI slots are becoming legacy support with PCI-Express becoming the standard. In addition, motherboards offer, at most, 7 slots while backplanes can offer up to 20 slots. In a backplane 12.3" wide, similar in size to an ATX motherboard at 12", a backplane with a Single Board Computer can offer 12 slots for I/O cards with virtually any mix of slot types.

Types, standards

Currently the most common variety of Single Board Computer in use is of a specific form factor similar to other full-size plug-in cards and is intended to be used in a backplane. Some architectures are dependent entirely on single-board computers, such as CompactPCI, PXI, VMEbus, VXI, PICMG architecture, etc. In the Intel PC world, the intelligence and interface/control circuitry is placed on a plug-in board that is then inserted into a passive (or active) backplane. The end result is similar to having a system built with a motherboard, except that the backplane determines the slot configuration. Backplanes are available with a mix of slots (ISA, PCI, PCIX, PCI-Express, etc), usually totaling 20 or less, meaning it will fit in a 19" rackmount enclosure (17" wide chassis).

Some single-board computers also exist as form factors that stack like building blocks, and do not have the form of a traditional backplane. Examples of stacking SBC form factors include PC/104, PC/104-Plus, PCI-104, EPIC, and EBX; these systems are commonly available for use in embedded control systems.

In the Intel Single Board Computer world, PICMG provides standards for the backplane interface: PICMG 1.0, 1.1 and 1.2^[1] provide for ISA and PCI support with 1.2 adding PCIX support PICMG 1.3^{[2] [3]} provides for PCI-Express support. Single Board Computers meeting the PICMG 1.3 specification are referred to as a System Host Board.

Stack-type SBCs often have memory provided on plug-cards such as SIMMs and DIMMs, however they can still be regarded as SBCs because although the memory modules are technically additional circuit boards, they have no extra functionality beyond providing memory and are basically just carriers for the RAM chips. Hard drive circuit boards are also not counted for determining if a computer is an SBC or not for two reasons, firstly because the HDD is regarded as a single block storage unit, and secondly because the SBC may not require a hard drive at all as most can be booted from their network connections.

Chassis Plans PICMG 1.3 Dual Quad Core Single Board Computer in BPX 3/8 Backplane

One of the first 10 MMD-1s, a prototype unit, produced by E&L Instruments in 1976. The "dyna-micro"/"MMD-1" was the world's first true "Single Board" computer. The MMD-1 had ALL components on a single Printed Circuit Board, including memory, I/O, user input device, and a display. Nothing external to the single board except power was required to both program and run the MMD-1. The original design of the MMD-1 was called the "dyna-micro", but it was soon re-branded as the "MMD-1"

Computer case

A computer case (also known as the computer chassis, cabinet, tower, box, enclosure, housing or simply case) is the enclosure that contains the main components of a computer. Cases are usually constructed from steel, aluminium, or plastic, although other materials such as wood and plexiglas have also been used in case designs. Often made of SECC steel.

A stripped ATX case lying on its side. The motherboard will lie flat on the bottom, against the right panel, with peripheral connectors protruding through the rear panel, drive bays at the top and front, and the power supply at the top and rear.

Sizes

Cases can come in many different sizes, or form factors. The size and shape of a computer case is usually determined by the form factor of motherboard that it is designed to accommodate, since this is the largest and most central component of most computers. Consequently, personal computer form factors typically specify only the internal dimensions and layout of the case. Form factors for rack-mounted and blade servers may include precise external dimensions as well, since these cases must themselves fit in specific enclosures.

For example, a case designed for an ATX motherboard and power supply may take on several external forms, such as a vertical tower (designed to sit on the floor) or a flat desktop or pizza box (designed to sit on the desk under the computer's monitor). Full-size tower cases are typically larger in volume than desktop cases, with more room for drive bays and expansion slots. Desktop cases—and mini-tower cases designed for the reduced microATX form factor—are popular in business environments where space is at a premium.^[1]

Currently, the most popular form factor for desktop computers is ATX, although microATX and small form factors have become very popular for a variety of uses. Companies like Shuttle Inc. and AOpen have popularized small cases, for which FlexATX is the most common motherboard size. Apple Computer has also produced the Mac Mini computer, which is similar in size to a standard CD-ROM drive.

There are mini-tower, midi-tower, big-tower/full-tower.

Layout

Computer cases usually include sheet metal enclosures for a power supply unit and drive bays, as well as a rear panel that can accommodate peripheral connectors protruding from the motherboard and expansion slots. Most cases also a power button or switch, a reset button, and LEDs to indicate power status, hard drive usage, and network activity. Some cases include built-in I/O ports (such as USB and headphone ports on the front of the case). Such a case will also include wires needed to connect these ports to the motherboard.

Major component locations

• The motherboard is usually screwed to the bottom or the side of the case (depending on the form factor and orientation).
• Form factors such as ATX provide a back panel with cut-out holes to expose I/O ports provided by integrated peripherals, as well as expansion slots which may optionally expose additional ports provided by expansion cards.
• The power supply unit is often housed at the top rear of the case; it is usually attached with four screws to support its weight.
• Most cases include drive bays on the front of the case; a typical ATX case includes both 5.25" and 3.5" bays. In modern computers, the former are used mainly for optical drives, while the latter are used for hard drives, floppy drives, and card readers.
• Buttons and LEDs are typically located on the front of the case; some cases include additional I/O ports, temperature and/or processor speed monitors in the same area.
• Vents are often found on the front, back, and sometimes on the side of the case to allow cooling fans to be mounted via surrounding threaded screw holes.

Internal access

Tower cases have either a single side panel which may be removed in order to access the internal components or a large cover that saddles the chassis. Traditionally, most computer cases required screws to hold components and panels in place (i.e. motherboard, PSU, drives, and expansion cards). Recently there is a trend toward "screwless" cases, in which components are held together with snap-in plastic rails, thumbscrews, and other methods that do not require tools; this facilitates quick assembly and modification of computer hardware.

Computer cases

A black mid or midi tower case (ATX form factor)

A beige mini tower case (microATX form factor)

Three of the Wikimedia servers in 1U rackmount cases

Enthusiast case featuring translucent panel casemod

Micro ATX Desktop case beside standard ATX tower case

Antec Fusion V2 home theater PC case with VFD display, volume control and some ports on front.

Appearance

The latest versions of Apple's iMacs place all of the computer's internal components behind an LCD screen. Save for the base, the iMac is about 1.25 inches thick. This miniaturization is achieved using parts designed for notebook computers.^{[citation needed]}

Through the 1990s, most computer cases had simple rectangular shapes, and were often painted beige. Beige box designs are still found on a large number of budget computers assembled from generic components.

The 1998 introduction of the Apple iMac led to greater enthusiasm for imaginative case designs^{[citation needed]}. Apple has continued to lead in the area of computer aesthetics, and has produced several innovative computers in small cases. Companies like Shuttle and AOpen have tapped the demand for small but customizable cases. The influence of these designs has led major OEM computer vendors, such as Dell and HP, to sell computers in more eye-catching cases, which may feature rounded edges, engraved logos, and translucent materials. Contemporary OEM computer cases have black or dark gray color, with metallic silver-colored accents.

Case modding is the artistic styling of computer cases, often to draw attention to the use of advanced or unusual components. Since the early 2000s, some cases have included clear side panels or acrylic windows so that users can look inside while it is operating. Modded cases may also include internal lighting, custom paint, or liquid cooling systems. Some hobbyists build custom cases from raw materials like aluminum, steel, acrylic, or wood.

Stickers are common on computer cases. These may advertise the manufacturer's logo, a list of the computer's specifications, the intended operating system (for example, "Designed for Windows XP"), the microprocessor used (such as Intel Inside) or, on homebuilt computers, any interest the builder may have. .

Prominent after-market case manufacturers include Ahanix, Antec, AOpen, Chieftec, Cooler Master, Ever Case, Foxconn, Gigabyte Technology, HEC Compucase, IXIUM, Lian Li, NZXT, OrigenAE, Raidmax, Shuttle Inc., SilverStone Technology, Thermaltake and Zalman.

Intrusion detection

Some computer cases include a biased switch (push-button) which connects to the motherboard. When the case is opened, the switch position changes and the system records this change. The system firmware or BIOS may be configured to report this event the next time it is powered-on.

This serves as a physical intrusion detection system and may help computer owners to detect tampering with their computer. However, most such systems are quite simple in construction; a knowledgeable intruder can open the case or modify its contents without triggering the switch.

Comparison of computer form factors

This article compares the IBM compatible personal computer motherboard form factors – that is, the different sizes and specific or de-facto standards of major system components. In all cases, at least the motherboard footprint, mounting, and connectorization is specified. Less frequently, dimensions for cases and power supplies is also standardized. Power supply voltages and current requirements may also be given.

The specifications are considered a form factor (as opposed to a model) when enough information is available so that FRU-level parts can be sourced from more than one OEM.

There are actually many computer form factors. These can generally be classified according to category of application (especially in embedded systems) or by architecture (e.g. CHRP). However, this comparison is limited to ISA (IBM compatible) PC architectures, compatible evolutions of it (legacy-free), or form factors that have evolved to accommodate ISA-compatible CPUs (e.g. -ITX and ETX).

Computer form factors

Name	PCB Size (mm)
WTX	356×425
AT	350×305
Baby-AT	330×216
BTX	325×266
ATX	305×244
LPX	330×229
NLX	254×228
microATX	244×244
DTX	244×203
FlexATX	229×191
Mini-DTX	203×170
EBX	203×146
microATX (Min.)	171×171
Mini-ITX	170×170
EPIC (Express)	165×115
Nano-ITX	120×120
COM Express	125×95
ETX / XTX	114×95
Pico-ITX	100×72
PC/104 (-Plus)	96×90
mobile-ITX	75×45

Overview of form factors

Pictorial comparison of some common computer form factors.

A PC motherboard is the main circuit board within a typical desktop computer, laptop or server. It has a number of functions of which the main ones are:

• As a central backbone to which all other modular parts (CPU, RAM, hard drives etc) can be attached as required to create a modern computer
• To accept (on many motherboards) different components (in particular CPU and PCI cards) for the purposes of customization.
• To distribute power to many of the PC components
• To electronically co-ordinate the operation of these, and interface all of these with one another.

As new generations of components have been developed, the standards of motherboards have changed too - for example with AGP being introduced, and more recently PCI Express. However the basic standardized size and layout of motherboard have changed much more slowly, and are controlled by their own standards. This is helped by the fact that in many ways, the list of components a motherboard must include changes far slower than the components themselves. For example, north bridge controllers have changed many times since their original introduction, with many manufacturers bringing out their own versions, but in terms of form factor standards, the requirement to allow for a north bridge has remained fairly static for many years.

Although it is a slower process, form factors do evolve regularly in response to changing demands. The original PC standard (AT) was superseded in 1995 by the current industry standard ATX, which still dictates the size and design of the motherboard in most modern PCs. The latest update to the ATX standard was released in 2004. A divergent standard by chipset manufacturer VIA called EPIA (aka -ITX, and not to be confused with EPIC) is based upon smaller form factors and its own standards.

Differences between form factors are most apparent in terms of their intended market sector, and involve variations in size, design compromises and typical features. Most modern computers have very similar requirements, so form factor differences tend to be based upon subsets and supersets of these. For example, a desktop computer may require more sockets for maximal flexibility and many optional connectors and other features on-board, whereas a computer to be used in a multimedia system may need to be optimized for heat and size, with additional plug-in cards being less common. The smallest motherboards may sacrifice CPU flexibility in favor of a fixed manufacturer's choice.

[edit] Comparisons

[edit] Tabular information

Form factor	Originated	Max. size	Typical feature-set (compared to ATX)	Typical CPU flexibility	Power handling	Notes (Typical usage, Market adoption, etc)
XT	IBM 1983	8.5 × 11" 216 × 279 mm				Obsolete - see Industry Standard Architecture. The IBM Personal Computer XT was the successor to the original IBM PC, its first home computer. As the specifications were open, many clone motherboards were produced and it became a de facto standard.
AT (Advanced Technology)	IBM 1984	12 × 11"–13" 305 × 279–330 mm				Obsolete - see Industry Standard Architecture. Created by IBM for the IBM Personal Computer/AT, an Intel 80286 machine. Also known as Full AT, it was popular during the era of the Intel 80386 microprocessor. Superseded by ATX.
Baby-AT	IBM 1985	8.5" × 10"–13" 216 mm × 254-330 mm				IBM's 1985 successor to the AT motherboard. Functionally equivalent to the AT, it became popular due to its significantly smaller size.
ATX	Intel 1996	12" × 9.6" 305 mm × 244 mm				Created by Intel in 1995. As of 2007, it is the most popular form factor for commodity motherboards. Typical size is 9.6x12" although some companies extend that to 10x12".
SSI CEB	SSI	12" × 10.5" 305 mm × 267 mm				Created by the Server System Infrastructure (SSI) forum. Derived from the EEB and ATX specifications. This means that SSI CEB motherboards have the same mounting holes and the same IO connector area as ATX motherboards.
microATX	1996	9.6" × 9.6" 244 mm × 244 mm				A smaller variant of the ATX form factor (about 25% shorter). Compatible with most ATX cases, but has fewer slots than ATX, for a smaller power supply unit. Very popular for desktop and small form factor computers as of 2007.
Mini-ATX	Intel	11.2" × 8.2" 284 mm × 208 mm
FlexATX	Intel 1999	9.0" x 7.5" 228.6 × 190.5 mm max.				A subset of microATX developed by Intel in 1999. Allows more flexible motherboard design, component positioning and shape. Can be smaller than regular microATX.
Mini-ITX	VIA 2001	6.7" × 6.7" 170 mm × 170 mm max.			100W max	A small, highly-integrated form factor, designed for small devices such as thin clients and set-top boxes.
Nano-ITX	VIA 2003	4.7" × 4.7" 120 mm × 120 mm
Pico-ITX	VIA 2007	100 mm × 72 mm max.
Mobile-ITX	VIA 2007	2.953"× 1.772" 75 mm × 45 mm
BTX (Balanced Technology Extended)	Intel 2004	12.8" × 10.5" 325 mm × 267 mm max.				A standard proposed by Intel as a successor to ATX in the early 2000s.
MicroBTX (or uBTX)	Intel 2004	10.4" × 10.5" 264 mm × 267 mm max.
PicoBTX	Intel 2004	8.0" × 10.5" 203 mm × 267 mm max.
DTX	AMD 2007	200 mm × 244 mm max.
Mini-DTX	AMD 2007	200 mm × 170 mm max.
smartModule	Digital-Logic	66 x 85 mm				Used in embedded systems and single board computers. Requires a baseboard.
ETX	Kontron	95 x 114 mm				Used in embedded systems and single board computers. Requires a baseboard.
Extended ATX (EATX)	?	12" × 13" 305mm × 330 mm				Used in rackmount server systems. Typically used for server-class type motherboards with dual processors and too much circuitry for a standard ATX motherboard. The mounting hole pattern for the upper portion of the board matches ATX.
LPX	?	9" × 11"–13" 229 mm × 279–330 mm				Based on a design by Western Digital, it allowed smaller cases than the AT standard, by putting the expansion card slots on a riser.[1] Used in slimline retail PCs. LPX was never standardized and generally only used by large OEMs.
Mini-LPX	?	8"–9" × 10"–11" 203–229 mm × 254–279 mm				Used in slimline retail PCs
PC/104	PC/104 Consortium 1992	3.8" × 3.6"				Used in embedded systems AT Bus architecture adapted to vibration-tolerant header connectors
PC104plus	PC/104 Consortium 1997	3.8" × 3.6"				Used in embedded systems PCI Bus architecture adapted to vibration-tolerant header connectors
PCI/104Express	PC/104 Consortium 2008	3.8" × 3.6"				Used in embedded systems PCI Express architecture adapted to vibration-tolerant header connectors
NLX	Intel 1999	8"–9" × 10"-13.6" 203–229 mm × 254–345 mm				A low-profile design released in 1997. It also incorporated a riser for expansion cards, and never became popular.
UTX	TQ-Components 2001	88 x 108 mm				Used in embedded systems and IPCs. Requires a baseboard.
WTX	Intel 1998	14" × 16.75" 355.6 mm × 425.4 mm				A large design for servers and high-end workstations featuring multiple CPUs and hard drives.
XTX	2005	95 x 114 mm				Used in embedded systems - requires a baseboard.

Graphical comparison of physical sizes

This image compares the sizes of common form factors to ISO 216 paper sizes (e.g. A4) (Sizes are in mm):

[edit] Visual examples of different form factors

Example images of different form factors

ATX (Abit KT7)

mini-ITX (VIA EPIA 5000AG)

Pico-ITX (VIA EPIA PX10000G)

PC/104 and EBX

PC/104 is an embedded computer standard which defines both a form factor and computer bus. PC/104 is intended for embedded computing environments. Single board computers built to this form factor are often sold by COTS vendors, which benefits users who want a customized rugged system, without months of design and paper work.

The PC/104 form factor was standardized by the PC/104 Consortium in 1992.[3] An IEEE standard corresponding to PC/104 was drafted as IEEE P996.1, but never ratified.

The 5.75 x 8.0 in. Embedded Board eXpandable (EBX) specification, which was derived from Ampro's proprietary Little Board form-factor, resulted from a collaboration between Ampro and Motorola Computer Group.

As compared with PC/104 modules, these larger (but still reasonably embeddable) SBCs tend to have everything of a full PC on them, including application oriented interfaces like audio, analog, or digital I/O in many cases. Also it's much easier to fit Pentium CPUs -- whereas it's a tight squeeze (or expensive) to do so on a PC/104 SBC. Typically, EBX SBCs contain: the CPU; upgradeable RAM subassemblies (e.g. DIMM); Flash memory for solid state disk; multiple USB, serial, and parallel ports; onboard expansion via a PC/104 module stack; off-board expansion via ISA and/or PCI buses (from the PC/104 connectors); networking interface (typically Ethernet); and video (typically CRT, LCD, and TV).

Mini PC

Mini PC is a PC form factor very close in size to an external CD or DVD drive.

Motherboard

Motherboard

The ASUS CUSL2-C motherboard

Connects to: Microprocessors via sockets Main memory via Slots Peripherals via one of External ports Internal cables

Form factors: ATX microATX Others

Common Manufacturers: ASUS Foxconn Intel Others

A motherboard is the central or primary printed circuit board (PCB) making up a complex electronic system, such as a modern computer. It is also known as a mainboard, baseboard, system board, planar board, or, on Apple computers, a logic board, and is sometimes abbreviated casually as mobo.^[1]

Most motherboards produced today are designed for so-called IBM-compatible computers, which held over 96% of the global personal computer market in 2005.^[2] Motherboards for IBM-compatible computers are specifically covered in the PC motherboard article.

A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane also contains the central processing unit and other subsystems such as real time clock, and some peripheral interfaces.

A typical desktop computer is built with the microprocessor, main memory, and other essential components on the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices are typically attached to the motherboard via edge connectors and cables, although in modern computers it is increasingly common to integrate these "peripherals" into the motherboard.

Components and functions

The 2004 K7VT4A Pro^[3] motherboard by ASRock. The chipset on this board consists of northbridge and southbridge chips.

The motherboard of a typical desktop consists of a large printed circuit board. It holds electronic components and interconnects, as well as physical connectors (sockets, slots, and headers) into which other computer components may be inserted or attached.

Most motherboards include, at a minimum:

• sockets (or slots) in which one or more microprocessors (CPUs) are installed^[4]
• slots into which the system's main memory is installed (typically in the form of DIMM modules containing DRAM chips)
• a chipset which forms an interface between the CPU's front-side bus, main memory, and peripheral buses
• non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system's firmware or BIOS
• a clock generator which produces the system clock signal to synchronize the various components
• slots for expansion cards (these interface to the system via the buses supported by the chipset)
• power connectors and circuits, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.^[5]

The Octek Jaguar V motherboard from 1993.^[6] This board has 6 ISA slots but few onboard peripherals, as evidenced by the lack of external connectors.

Additionally, nearly all motherboards include logic and connectors to support commonly-used input devices, such as PS/2 connectors for a mouse and keyboard. Early personal computers such as the Apple II or IBM PC included only this minimal peripheral support on the motherboard. Occasionally video interface hardware was also integrated into the motherboard; for example on the Apple II, and rarely on IBM-comatible computers such as the IBM PC Jr. 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 heatsinks and mounting points for fans to dissipate excess heat.

Integrated peripherals

Diagram of a modern motherboard, which supports many on-board peripheral functions as well as several expansion slots.

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.

For example, the ECS RS485M-M,^[7] a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

• disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)
• integrated ATI Radeon graphics controller supporting 2D and 3D graphics, with VGA and TV output
• integrated sound card supporting 8-channel (7.1) audio and S/PDIF output
• fast Ethernet network controller for 10/100 Mbit networking
• USB 2.0 controller supporting up to 12 USB ports
• IrDA controller for infrared data communication (e.g. with an IrDA enabled Cellular Phone or Printer)
• temperature, voltage, and fan-speed sensors that allow software to monitor the health of computer components

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago, however as of April 2007 such highly-integrated motherboards are available for as little as $30 in the USA.

Temperature and reliability

Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the northbridge, in modern motherboards. 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 their heatsinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional case fans as well. Newer motherboards have 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.

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 careful layout of the motherboard and other components to allow for heat sink placement.

A 2003 study^[8] 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.^[9]

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 105 °C,^[10] their expected design life roughly doubles for every 10 °C below this. At 45 °C a lifetime of 15 years can be expected. This appears reasonable for a computer motherboard, however many manufacturers have delivered substandard capacitors, which significantly reduce this life expectancy. Inadequate case cooling and elevated temperatures easily exacerbate this problem. It is possible, but tedious and time-consuming, to find and replace failed capacitors on PC motherboards; it is less expensive to buy a new motherboard than to pay for such a repair.

History

Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or mainframe with components connected by a backplane consisting of a set of slots themselves connected with wires; in very old designs the wires were discrete connections between card connector pins, but printed-circuit boards soon became the standard practice. The central processing unit, memory and peripherals were housed on individual printed circuit boards which plugged into the backplane.

During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see above). In the late 1980s, motherboards began to include single ICs (called Super I/O chips) capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. As of the late 1990s, many personal computer motherboards support a full range of 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 retain only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

Popular personal computers such as the Apple II and IBM PC had published schematic diagrams and other documentation which permitted rapid reverse-engineering and third-party replacement motherboards. Usually intended for building new computers compatible with the exemplars, many motherboards offered additional performance or other features and were used to upgrade the manufacturer's original equipment.

Bootstrapping using the BIOS

Motherboards contain some non-volatile memory to initialize the system and load an operating system from some external peripheral device. Microcomputers such as the Apple II and IBM PC used read-only memory chips, mounted in sockets on the motherboard. At power up the central processor would load its program counter with the address of the boot ROM and start executing ROM instructions displaying system information on the screen and running memory checks, which would in turn start loading memory from an external or peripheral device (disk drive) if one isn't available then the computer can perform tasks from other memory stores or displays an error message depending on the model and design of the computer and version of the bios.

Most modern motherboard designs use a BIOS, stored in a EEPROM chip soldered to the motherboard, to bootstrap the motherboard. (Socketed BIOS chips are widely used, also.) By booting the motherboard, the memory, circuitry, and peripherals are tested and configured. This process is known as a Power On Self Test or POST. Errors during POST result in POST error codes, ranging from simple audible beeps from the speaker to complex diagnostic messages displayed on the video monitor.

The BIOS often requires configuration settings to be stored on the motherboard. Since configuration settings must be easily edited, these settings are often stored in non-volatile RAM (NVRAM) rather than in some sort of read-only memory (ROM). When a user makes configuration changes or alters the date and time of the computer, this small NVRAM circuit stores the data. Typically, a small, long-lasting battery (e.g. a lithium coin cell CR2032) is used to keep the NVRAM "refreshed" for many years. Therefore, a failing battery on a motherboard will produce the symptoms of a computer that cannot determine the correct date and time, nor remember what hardware configuration the user has selected. The BIOS itself is unaffected by the status of the battery.

When IBM first introduced the PC in the 1980s, imitations were quite common. (The physical parts which made up the motherboard were trivial to acquire.) However, the imitations were never successful until the IBM ROM BIOS was legally copied.^[11] To understand why copying the BIOS was an important step, consider that the BIOS contained vital instructions which interacted with peripherals. Without these software instructions in the BIOS, a PC would not function properly. (In most modern computer operating systems, the BIOS is bypassed for most hardware functions, but in the 1980s, the BIOS served many vital low-level functions.)

So when Compaq Computer Corp. spent US$1 million to clone the IBM BIOS using reverse engineering, they became an elite computer manufacturer of IBM PC Clones. Phoenix Technology soon matched their feat and began reselling BIOSes to other clone makers.^[12] It has been noted that Microsoft was more than happy to license the operating system (DOS), and IBM was more than happy to sue companies^[13] that violated the copyright of their BIOS. But by documenting and publicizing the reverse engineering of the BIOS, Compaq and Phoenix were legally competing with IBM using their own copyrighted BIOS.

Once the bootstrapping of the computer's peripherals are complete, the BIOS will normally pass control to another set of instructions stored on a bootable device.

Devices which are normally used to boot a computer:

• floppy drive
• network controller
• CD-ROM drive
• DVD-ROM drive
• SCSI hard drive
• IDE, EIDE, or SATA hard drive
• External USB memory storage device

Any of the above devices can be stored with machine code instructions to load an operating system or a program.

Form factors

Motherboards are produced in a variety of sizes and shapes ("form factors"), some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible commodity computers have been standardized to fit various case sizes. As of 2007, most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers which have not traditionally been built from commodity components.

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 due to the large number of integrated components.