Motherboard
CPU sockets
A CPU socket or slot is an electrical component that attaches to a printed circuit board (PCB) and is designed to house a CPU (also called a microprocessor). 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 (as well as reducing cost), 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 (laptops typically use surface mount CPUs), particularly those based on the Intel
x86 architecture. A CPU socket type and motherboard chipset must support the CPU series and speed.
ntegrated peripherals
Block 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,
[5] a typical modern budget motherboard for computers based on
AMD processors, has on-board support for a very large range of peripherals:
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 US.
Peripheral card slots
A typical motherboard of 2009 will have a different number of connections depending on its standard.
A standard ATX motherboard will typically have one PCI-E 16x connection for a graphics card, two conventional PCI slots for various expansion cards, and one PCI-E 1x (which will eventually supersede
PCI). A standard
EATX motherboard will have one PCI-E 16x connection for a graphics card, and a varying number of PCI and PCI-E 1x slots. It can sometimes also have a PCI-E 4x slot. (This varies between brands and models.)
Some motherboards have two PCI-E 16x slots, to allow more than 2 monitors without special hardware, or use a special graphics technology called
SLI(for
Nvidia) and
Crossfire (for
ATI). These allow 2 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming,video editing etc.
As of 2007, virtually all motherboards come with at least four
USB ports on the rear, with at least 2 connections on the board internally for wiring additional front ports that may be built into the computer's case.
Ethernet is also included. This is a standard networking cable for connecting the computer to a
network or a
modem. A sound chip is always included on the motherboard, to allow sound output without the need for any extra
components. This allows computers to be far more
multimedia-based than before. Some motherboards contain video outputs on the back panel for integrated graphics solutions (either embedded in the motherboard, or combined with the microprocessor, such as the Intel HD Graphics). A separate card may still be used.
[edit]Temperature and reliability
Motherboards are generally
air cooled with
heat sinks often mounted on larger chips, such as the
Northbridge, in modern motherboards. Insufficient or improper cooling can cause damage to the internal components of the computer and 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 their
heat sinks, 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 computers (which typically have high-performance microprocessors, large amounts of
RAM, and high-performance
video cards) 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 careful layout of the motherboard and other
components to allow for heat sink placement.
A 2003 study
[6] 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.
[7]
A microATX motherboard with some faulty capacitors.
- For more information on premature capacitor failure on PC motherboards, see capacitor plague.
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,
[8] 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,
[9] which significantly reduce 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.
[edit]Form factor
Motherboards are produced in a variety of sizes and shapes called
computer form factor, some of which are specific to individual
computer manufacturers. However, the motherboards used in IBM-compatible systems are designed to fit various
case sizes. As of 2007, most
desktop computer motherboards use one of these
[which?] standard form factors—even those found in
Macintosh and
Sun computers, which have not been built from commodity components. A case's motherboard and PSU 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 due to the large number of integrated components.
[edit]Bootstrapping using the BIOS
Further information:
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
ROM 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. These instructions displayed system information on the screen, ran memory checks, and then loaded an operating system from an external or peripheral device (disk drive). If none was available, then the computer would perform tasks from other memory stores or display 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 an
EEPROM chip soldered or socketed to the motherboard, to
bootstrap an
operating system. When power is first applied to the motherboard, the BIOS firmware tests and configures memory, circuitry, and peripherals. This
Power-On Self Test (POST) may include testing some of the following things:
On recent motherboards, the BIOS may also patch the central processor microcode if the BIOS detects that the installed CPU is one in for which
errata has been published. Many of the above devices can be stored with
machine code instructions to load an
operating system or
program.
[edit]See also
