07-06-2009, 01:11 AM
Motherboard, Processor and Memory form the main components of a computer system. The motherboard is the circuit board to which all the other components of the computer connect in some way. The video card, sound card, IDE hard drive, etc. all plug into the motherboard's various slots and connectors. The CPU also plugs into the motherboard via a Socket or a Slot. Motherboard is the main circuit board of a computer. It contains connectors and ports for attaching additional boards and peripheral devices. It has multiple controller chips on the motherboard to control standard devices such as keyboard, disk drive, etc. All the controller chips together are called as chipset. The Motherboard is the main circuit board of a computer. The motherboard contains the connectors for attaching additional components. The collection of chips and controllers is known as the 'chipset'. The motherboard is a collection of devices that control the flow of data and operating electricity for all the primary components in a PC. The Motherboard has two main processing chips on it called the Northbridge and the Southbridge. The Northbridge handles all the data flows to and from the main memory and also all the CPU transactions. The Southbridge handles the data for most of the ports. CLASSIFICATION-: # Integrated and nonintegrated are the two major types of Motherboards based on the way components were installed or designed on it. . 1.Integrated system boards have most of the components included into the motherboard circuitry that would otherwise be installed as expansion cards, thus the name integrated. Integrated system boards were designed for their simplicity. A major drawback is that even in case one component breaks down then the entire motherboard needs to be replaced. Though they are cheaper to produce, they are more expensive to repair. ATX mother boards are common integrated motherboards. 2. Nonintegrated motherboards have lot of expansion cards. The major components are the video card, disk controllers. Nonintegrated motherboards can be easily identified because each expansion slot is usually occupied by one of the components. Nonintegrated system boards are further classified based on their form factors (design): mainly into 2 types AT and ATX. The AT motherboards are the first modern form factor to be widely used. AT stands for Advanced Technology & it was released by IBM in 1984. The PC and XT form factors that preceded it were quite uncommon. There are a few computers that still use AT and its variant Baby AT, but current standards are in favor of ATX. AT was not a huge technological advancement from older form factors. The biggest advancement was the 'tower' design and a power switch in the front. The AT power supply provided 192 watts, thrice more than older form factors. The AT motherboard is 12 inches (305 mm) and it won't fit in 'mini-tower cases' or 'mini desktop'. One of the major problems with the width of this board it takes up space behind the drive bays making installation of new drives difficult. The power connectors for AT motherboards are almost identical with 6-pin cords. The two connectors are not physically distinguishable, leading to damage of the motherboard when they were connected incorrectly. Baby AT is a variant of AT, introduced by IBM in 1985. Baby AT motherboards were popular as they were cheaper and smaller. These motherboards have the same functionality as AT motherboards but the width is reduced from 12' to 8.5' and are marginally longer. AT and Baby AT motherboards were the first PC motherboards to have built in sockets (headers) for I/O ports (serial, parallel, etc.). The serial and parallel port connectors are usually attached using cables that go between the physical connectors mounted on the back of the case and headers (pin connectors). These motherboards are distinguished by their shape, and by the presence keyboard connector soldered onto the motherboard. They were widely used in 386, 486 and early Pentium computers. The AT and Baby AT form factors have the processor socket(s)/slot(s) and memory sockets at the front of the motherboard. Long expansion cards and drives were designed to extend over them. Older processors and memory chips were small and put directly onto the motherboard. As processors became larger, the form factor did not have space to fit the combination of processor, heat sink, and fan. The introduction of SIMM/DIMM sockets, the concept of direct memory installation became obsolete. The ATX form factor was later on designed by Intel in order to overcome the above issues. ATX Motherboards that were introduced in 1995 quickly replaced older Baby AT & AT computers. ATX (Advanced Technology EXtended motherboard) improves on the previous Baby AT & AT form factors, by rotating the orientation of the board 90 degrees. This allowed for a more efficient design, with disk drive cable connectors nearer to the drive bays and the CPU closer to the power supply and cooling fan. ATX is not an abbreviation and is actually a trademark that belongs to Intel. The ATX uses a new specification of power supply that can be powered on or off by a signal from the motherboard. This allows notebook-style power management and software-controlled shutdown and power-up. A 3.3V output is also provided directly from the power supply. The ATX power supply has a side vent that blows air from the outside directly across the processor and memory modules, allowing passive heatsinks to be used in most cases, thereby reducing system noise. Mini-ATX is simply a smaller version of a full-sized ATX board. The AT standard had only a keyboard connector. Other common I/O connectors (serial & parallel ports etc) had to be mounted individually. The ATX was the first computer motherboard to not only include I/O support (serial, parallel, mouse, etc.), but to place all the connectors directly (soldered) onto the motherboard. ATX allowed each motherboard manufacturer to put these ports in a rectangular area on the back of the system, with an arrangement they could define themselves. Prior to the ATX, only the keyboard connector was attached to the motherboard. AT-style computer cases had a power button that was directly connected to the system power supply unit (PSU). The Power could be managed with proper BIOS support. Instead of two similar-looking power connectors (that could sometimes be misconnected causing short-circuits) ATX used one large 20-pin power connector, which made installation much easier and safer. The newer ATX specification defines a 24-pin power connector to support the power requirements of PCI Express. Maximum measures of ATX board are 12' x 9.6' (305mm x 244mm). A Full ATX is 12' wide x 9.6' deep & a Mini-ATX is 11.2' wide x 8.2' deep. Apart from above mentioned advantages ATX form factors also provides Improved Design for Upgradeability, Reduces Drive Bay Interference, Reduces Expansion Card Interference & has Better Air Flow. Some related designs include mini-ATX and microATX. MicroATX offers same benefits as ATX form factor but by reducing the physical size of the motherboard it improved the overall system design costs. This was done by reducing the number of I/O slots supported on the board. The microATX form factor provides more space at the rear to reduce emissions from using integrated I/O connectors. ATX will eventually be replaced by BTX. NLX is a new form factor used in 'low profile' motherboard types. They have a unique design where the expansion slots are placed sideways on a special riser card to optimally use the space. . Some manufactures design and manufacture their own motherboard designs, which don't conform to either standard. Basically, the components are laid out differently than an AT or ATX, but it will work as a PC. Such motherboard is known as a proprietary design motherboard. The BTX (Balanced Technology Extended) form factor will to be the replacement for the ATX form factor. It was proposed by Intel to address some of the issues that arose from using newer technologies, which demand more power and produce more heat on motherboards compliant with the ATX specification. How motherboard Works The motherboard's main job is to hold the computer's microprocessor chip and let everything else connect to it. Everything that runs the computer or enhances its performance is either part of the motherboard or plugs into it via a slot or port. A motherboard allows all the parts of your computer to receive power and communicate with one another. The shape and layout of a motherboard is called the form factor. The form factor affects where individual components go and the shape of the computer's case. There are several specific form factors that most PC motherboards use so that they can all fit in standard cases. The form factor is just one of the many standards that apply to motherboards. Some of the other standards include: The socket for the microprocessor determines what kind of Central Processing Unit (CPU) the motherboard uses. The chipset is part of the motherboard's logic system and is usually made of two parts - the northbridge and the southbridge. These two 'bridges' connect the CPU to other parts of the computer. The Basic Input/Output System (BIOS) chip controls the most basic functions of the computer and performs a self-test every time you turn it on. Some systems feature dual BIOS, which provides a backup in case one fails or in case of error during updating. The real time clock chip is a battery-operated chip that maintains basic settings and the system time. The slots and ports found on a motherboard include: Peripheral Component Interconnect (PCI)- connections for video, sound and video capture cards, as well as network cards Accelerated Graphics Port (AGP) - dedicated port for video cards. Integrated Drive Electronics (IDE) - interfaces for the hard drives Universal Serial Bus or Firewire - external peripherals Memory slots Some motherboards also incorporate newer technological advances: Redundant Array of Independent Discs (RAID) controllers allow the computer to recognize multiple drives as one drive. PCI Express is a newer protocol that acts more like a network than a bus. It can eliminate the need for other ports, including the AGP port. Rather than relying on plug-in cards, some motherboards have on-board sound, networking, video or other peripheral support. In the early days of PC computers, all processors had the same set of pins that would connect the CPU to the motherboard, called the Pin Grid Array (PGA). These pins fit into a socket layout called Socket 7. This meant that any processor would fit into any motherboard. Today, however, CPU manufacturers Intel and AMD use a variety of PGAs, none of which fit into Socket 7. As microprocessors advance, they need more and more pins, both to handle new features and to provide more and more power to the chip. Current socket arrangements are often named for the number of pins in the PGA. Commonly used sockets are: Socket 478 - for older Pentium and Celeron processors Socket 754 - for AMD Sempron and some AMD Athlon processors Socket 939 - for newer and faster AMD Athlon processors Socket AM2 - for the newest AMD Athlon processors Socket A - for older AMD Athlon processors The newest Intel CPU does not have a PGA. It has an LGA, also known as Socket T. LGA stands for Land Grid Array. An LGA is different from a PGA in that the pins are actually part of the socket, not the CPU. The chipset is the 'glue' that connects the microprocessor to the rest of the motherboard and therefore to the rest of the computer. On a PC, it consists of two basic parts -- the northbridge and the southbridge. All of the various components of the computer communicate with the CPU through the chipset. The northbridge connects directly to the processor via the front side bus (FSB). A memory controller is located on the northbridge, which gives the CPU fast access to the memory. The northbridge also connects to the AGP or PCI Express bus and to the memory itself. The southbridge is slower than the northbridge, and information from the CPU has to go through the northbridge before reaching the southbridge. Other busses connect the southbridge to the PCI bus, the USB ports and the IDE or SATA hard disk connections. Chipset selection and CPU selection go hand-in-hand, because manufacturers optimize chipsets to work with specific CPUs. The chipset is an integrated part of the motherboard, so it cannot be removed or upgraded. This means that not only must the motherboard's socket fit the CPU, the motherboard's chipset must work optimally with the CPU. A bus is simply a circuit that connects one part of the motherboard to another. The more data a bus can handle at one time, the faster it allows information to travel. The speed of the bus, measured in megahertz (MHz), refers to how much data can move across the bus. Bus speed usually refers to the speed of the front side bus (FSB), which connects the CPU to the northbridge. FSB speeds can range from 66 MHz to over 800 MHz. Since the CPU reaches the memory controller though the northbridge, FSB speed can dramatically affect a computer's performance. Here are some of the other busses found on a motherboard: The back side bus connects the CPU with the level 2 (L2) cache, also known as secondary or external cache. The processor determines the speed of the back side bus. The memory bus connects the northbridge to the memory. The IDE or ATA bus connects the southbridge to the disk drives. The AGP bus connects the video card to the memory and the CPU. The speed of the AGP bus is usually 66 MHz. The PCI bus connects PCI slots to the southbridge. On most systems, the speed of the PCI bus is 33 MHz. Also compatible with PCI is PCI Express, which is much faster than PCI but is still compatible with current software and operating systems. PCI Express is likely to replace both PCI and AGP busses. A motherboard's memory slots directly affect what kind and how much memory is supported. Just like other components, the memory plugs into the slot via a series of pins. The memory module must have the right number of pins to fit into the slot on the motherboard. Evolution: The original PC had a minimum of integrated devices, just ports for a keyboard and a cassette deck (for storage). Everything else, including a display adapter and floppy or hard disk controllers, were add-in components, connected via expansion slots. Over time, more devices have been integrated into the motherboard. It's a slow trend though, as I/O ports and disk controllers were often mounted on expansion cards as recently as 1995. Other components - typically graphics, networking, SCSI and sound - usually remain separate. Many manufacturers have experimented with different levels of integration, building in some or even all of these components. However, there are drawbacks. It's harder to upgrade the specification if integrated components can't be removed, and highly integrated motherboards often require non-standard cases. Furthermore, replacing a single faulty component may mean buying an entire new motherboard. Consequently, those parts of the system whose specification changes fastest - RAM, CPU and graphics - tend to remain in sockets or slots for easy replacement. Similarly, parts that not all users need, such as networking or SCSI, are usually left out of the base specification to keep costs down. The basic changes in motherboard form factors over the years are covered later in this section - the diagrams below provide a detailed look at the various components on two motherboards. The first a Baby AT design, sporting the ubiquitous Socket 7 processor connector, circa 1995. The second is an ATX design, with a Pentium II Slot 1 type processor connector, typical of motherboards on the market in late 1998. BIOS The All motherboards include a small block of Read Only Memory (ROM) which is separate from the main system memory used for loading and running software. The BIOS will most likely be stored in a 32-pin chip, which can typically be identified by a silver or gold sticker that shows the name of the BIOS company - such as AMIBIOS, AWARD or Phoenix - and a code that indicates the version of code it contains. If its rectangular in shape, it's what is known as a DIP (Dual In-line Package) chip. Older motherboards may have 28-pin DIP BIOS chips. If your BIOS chip is square with connections on all four sides, it is in a PLCC (Plastic Leaded Chip Carrier) package. The ROM contains the PC's Basic Input/Output System (BIOS). This offers two advantages: the code and data in the ROM BIOS need not be reloaded each time the computer is started, and they cannot be corrupted by wayward applications that write into the wrong part of memory. If you have a DIP or PLCC chip that's actually soldered to your motherboard, you'll not be able to upgrade it by replacing the ROM. Modern-day BIOSes are flash upgradeable, meaning they may be updated via a floppy diskette to ensure future compatibility with new chips, add-on cards etc. The BIOS comprises several separate routines, serving different functions. The first part runs as soon as the machine is powered on. It inspects the computer to determine what hardware is fitted and then conducts some simple tests to check that everything is functioning normally - a process called the power-on self test (POST). If any of the peripherals are plug and play devices, it's at this point that the BIOS assigns their resources. There's also an option to enter the Setup program. This allows the user to tell the PC what hardware is fitted, but thanks to automatic self-configuring BIOSes this isn't used so much now. If all the tests are passed, the ROM then tries to determine which drive to boot the machine from. Most PCs ship with the BIOS set to check for the presence of an operating system in the floppy disk drive first (A
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