A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer . It is also known as a mainboard , baseboard , system board , or, on Apple computers, a logic board , and is sometimes abbreviated as mobo .

The basic purpose of the motherboard, like a backplane , is to provide the electrical and logical connections by which the other components of the system communicate.

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

The motherboard of a typical desktop consists of a large PCB . 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 in which one or more CPUs are installed
• 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.

The motherboard of a typical desktop consists of a large PCB . 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 in which one or more CPUs are installed
• 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.

HISTORY:

Motherboards are produced in a variety of 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.

These are some of the more popular motherboard form factors:

• PC/XT - created by IBM for the IBM PC , its first home computer. As the specifications were open, many clone motherboards were produced and it became a de facto standard.
• AT form factor (Advanced Technology) - created by IBM for its PC/XT successor, the AT . Also known as Full AT, it was popular during the era of the Intel 80386 microprocessor. Superseded by ATX.
• Baby AT - IBM's 1985 successor to the AT motherboard. Functionally equivalent to the AT, it became popular due to its significantly smaller size.
• ATX - created by Intel in 1995. As of 2007 , it is the most popular form factor for commodity motherboards.
• ETX - used in embedded systems and single board computers .
• microATX - a smaller variant of the ATX form factor (about 25% shorter). It is compatible with most ATX cases, but supports fewer expansion slots due to its smaller size. Very popular for desktop and small form factor computers as of 2007 .
• FlexATX - a subset of microATX developed by Intel in 1999. Allows more flexible motherboard design, component positioning and shape.
• LPX - based on a design by Western Digital , it allowed smaller cases than the AT standard, by putting the expansion card slots on a riser ( image ). LPX was never standardized and generally only used by large OEMs .
• NLX - a low-profile design released in 1997. It also incorporated a riser for expansion cards, and never became popular.
• BTX (Balanced Technology Extended) - a standard proposed by Intel as a successor to ATX in the early 2000s.
• Mini-ITX - a small, highly-integrated form factor created by VIA in 2001. Mini-ITX was designed for small devices such as thin clients and set-top boxes .
• WTX - created by Intel in 1998. A large design for servers and high-end workstations featuring multiple CPUs and hard drives .

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.

Socket A

Socket A (also known as Socket 462 ) is the CPU socket used for AMD processors ranging from the Athlon Thunderbird to the Athlon XP/MP 3200+, and AMD budget processors including the Duron and Sempron . Socket A also supports the recent AMD Geode NX embedded processors (derived from the Mobile Athlon XP ). The socket is a zero insertion force pin grid array type with 453 pins (nine pins are blocked in the socket to prevent accidental insertion of Socket 370 CPUs, hence the number 462). The front side bus frequencies supported for the AMD Athlon XP and Sempron are 133 MHz, 166 MHz, and 200 MHz.

AMD recommends that the weight of a Socket A CPU cooler not exceed 300  grams (10.6  ounces ). Heavier coolers may result in damage to the die when the system is not properly handled.

Socket A has been discontinued in favor of Socket 754 , Socket 939 , and recently Socket AM2 , except for its use with Geode NX processors. However, microprocessors and motherboards are still available from many vendors.

Technical specifications

• Support of processor clock-speeds between 600 MHz (Duron) to 2333 MHz (Athlon XP 3200+)
• Double data rate 100, 133, 166 and 200 MHz front side bus on Duron, XP and Sempron processors, based on the DEC lpha EV6 bus

Socket A mechanical load limits

All socket A processors(Athlon, Sempron, Duron and Geode NX) have the following mechanical maximum load limits which should not be exceeded during heatsink assembly, shipping conditions, or standard use. Load above those limits will crack the processor die and make it unusable.

Those load limits are quite small compared to the load limits of Socket 478 processors. Indeed they were so small that many users ended up with cracked processors while trying to remove or attach a heatsink to their fragile processor. It must be noted though that many processors were cracked from non standard or non certified heatsink solutions as those processors were not only shipped without qualified heatsinks, but without heatsinks at all as they were sold in trays.

Socket 478

In computing , Socket 478 is a type of CPU socket used for Intel 's Pentium 4 and Celeron series CPUs . Socket 478 was phased out with the launch of LGA775 .

Socket 478 has been used for all of the Northwood Pentium 4s and Celerons, the first Prescott Pentium 4s, and some Willamette Celerons and Pentium 4s. Socket 478 also supports newer Prescott Celeron Ds, and early Pentium 4 Extreme Edition processors with 2MB of L3 cache and some Core Duos . The socket was launched with the Northwood core to compete with AMD 's 462-pin Socket A and their Athlon XP processors. Socket 478, which accommodates high and low-end processors, was also the replacement for Socket 423 , a Willamette processor socket which remained in the market for only a short time.

Motherboards that use this socket support DDR , RDRAM , and in some cases SDRAM . However, the majority of boards are DDR based. Initial motherboards only supported RDRAM, however RDRAM is quite expensive, compared to DDR and SDRAM, and consumers demanded an alternative, thus DDR and SDRAM boards were made. Later revisions to chipsets that support Socket 478 added higher FSB speeds, higher DDR speeds, and support for dual channel DDR.

Like the previous Socket 423, Socket 478 is based on Intel's Quad Data Rate technology, with data transferring at four times the clock rate of its Front Side Bus. As such, the 400 MT/s bus was based on a 100 MHz clock signal, but was still able to provide 3.2GB/s of data to the chipset. At its release, no SDRAM product was capable of supporting so high a data rate, so Intel pushed forward RDRAM technology, with two channels of PC800 providing synchronous data capability. Poor consumer acceptance of expensive RDRAM lead Intel to release low-performance PC133-supporting chipsets, and finally DDR chipsets.

While the original 400 MT/s bus matched the data rate of PC3200, this bus speed was already outdated by the time PC3200 became available. Dual-channel memory was introduced on later chipsets, so that a matched pair of PC3200 modules was able to match the final 800 MT/s FSB.

The Celeron D is also available for Socket 478 and they are now the only CPU's still made for the socket. They use a quad-pumped 133MHz Bus Giving A 533MT/s FSB. They are available with 256KB L2 Cache and are built on the 90nm manufacturing process, using the Prescott Core.

Socket 478 is officially known by Intel as FC-PGA2. While Core Duo is available in a 478-pin package, that socket is different: micro FC-PGA, which was also used for earlier Pentium M and Celeron M processors. Core Duo is also available in a 479-ball (not pin) package known as micro FC-BGA.