A typical motherboard of 2009 will have a different number of connections
depending on its standard. A standard ATX motherboard will typically have 1x
PCI-E 16x connection for a graphics card, 2x PCI slots for various expansion
cards and 1x PCI-E 1x which will eventually supersede PCI.
A standard Super ATX motherboard will have 1x PCI-E 16x connection for a
graphics card. It will also have 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 2x PCI-E 16x slots, to allow more than 2 monitors
without special hardware or to allow use of 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 and video-editing.
As of 2007, virtually all motherboards come with at least 4x USB ports on the
rear, with at least 2 connections on the board internally for wiring additional
front ports that are built into the computer's case. Ethernet is also included
now. 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 to be output without the need for any extra components. This allows
computers to be far more multimedia-based than before. Cheaper machines now
often have their graphics chip built into the motherboard rather than a separate
card.
Temperature and reliability
Motherboards are generally air cooled with heat sinks often mounted on larger
chips, such as the northbridge, in modern motherboards. If the motherboard is
not cooled properly, it can cause the computer 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 higher-powered computers (which typically
have high-performance processors and large amounts of RAM, as well as
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 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.
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, 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 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.
Form factor
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[update], 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.
Nvidia SLI and ATI Crossfire
Nvidia SLI and ATI Crossfire technology allows two or more of the same series
graphics cards to be linked together to allow faster graphics-processing
capabilities. Almost all medium- to high-end Nvidia cards and most high-end ATI
cards support the technology.
They both require compatible motherboards. There is an obvious need for 2x
PCI-E 16x slots to allow two cards to be inserted into the computer. The same
function can be achieved in 650i motherboards by NVIDIA, with a pair of x8
slots. Originally, tri-Crossfire was achieved at 8x speeds with two 16x slots
and one 8x slot; albeit at a slower speed. ATI opened the technology up to Intel
in 2006, and all new Intel chipsets now support Crossfire.
SLI is a little more proprietary in its needs. It requires a motherboard with
Nvidia's own NForce chipset series to allow it to run (exception: select Intel
X58 chipset based motherboards).
It is important to note that SLI and Crossfire will not usually scale to 2x
the performance of a single card when using a dual setup. They also do not
double the effective amount of VRAM or memory bandwidth.
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 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,
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 none is available, then the computer can 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
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 computer
Power-On Self Test (POST) and may include testing some of the following devices:
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.
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