Computer Motherboard • Motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, w hile providing connectors for other peripherals. The motherboard is sometimes alternatively know n as the main board, syst em board, or, on Apple computers, the logic board. It is also sometimes casually shortened to mobo. • It has three basic functions 1. The motherboard serves to connect all of the parts of a computer together. All other components of the system communicate or transfer information to each other via motherboard. 2. The CPU, memory, hard drives, optical drives, video card, sound card and other ports and expansion cards all connect to the motherboard directly or via cables. It also houses the BIOS (Basic Input/Output System), w hich is the simple softw are run by a computer w hen initially turned on. 3. All other electronic components obtain electric voltages via motherboard. Motherboards, cases and pow er supplies all come in different sizes called form factors. All three must be compatible to w ork properly together. Internal components of motherboard • Modern motherboards include, at a minimum: 1. Sockets (or slots) in w hich one or more microprocessors are installed 2. Slots into w hich the system's main memory is installed (typically in the form of DIMM modules containing DRAM chips) 3. Achipset w hich forms an interface betw een the CPU's front-side bus, main memory, and peripheral buses 4. Non-volatile memory chips (usually Flash ROM in modern motherboards) containing the syst em' s firmw are or BIOS 5. A clock generator w hich produces the system clock signal to synchronize the various components 6. Slots for expansion cards (these interface to the system via the buses supported by the chipset) 7. Power connectors, w hich receive electrical pow er from the computer pow er supply and distribute it to the CPU, chipset, main memory, and expansion cards. 8. Connectors to support commonly-used input devices, such as PS/2 connectors for a mouse and keyboard. Fig-1 PC Motherboard • Chipset: - is logic circuit that is the intelligence of motherboard. It controls data transfer betw een the processor, cache, system buses, and peripherals. It has major impact on PC’s quality, feature set and speed.Most Modern Motherboareds has tw o chiptes connected as show n below . Fif-2 Connection Diagram of thenorthbridge and southbridgein modern motherboard. • CPU socket or slot- is an electrical component that attaches to a printed circuit board and is designed to house a CPU. The type of socket or slot (it has st andard) on the motherboard determines the type of processor that can be used. Fig-3 The Socket 370 processor socket, a ZIF type PGA socket • RAM connectors- RA M (Random Access Memory) is used to st ore data w hile the computer is running; how ever, its contents are w iped out as soon as the computer is switched off or restarted, as opposed to mass storage devices such as hard drives, w hich keep information safe even w hile turned off. This is w hy RAM is called " volatile." • Expansion slots are compartments into w hich expansion cards can be inserted. These are cards w hich give the computer new features or increased performance. There are several types of slots such as ISA, PCI, VLB, AGP, PCI Express, AMR, etc. • BIOS (Basic Input/Output System)-is the basic program used as an interface betw een the operating system and the motherboard. The BIOS is stored in ROM (read-only memory, w hich cannot be rew ritten), so it uses data contained w ithin the CMOS to find out w hat the system's hardw are configuration. • Cmos clock and battery- is real time clock (or RTC for short)- is a circuit which synchronizes system signals. It is made from a crystal which, as it vibrates, gives off pulses (called timer ticks) in order to keep the system elements running on the same time. Fig-4 Main component of motherboard External components of Motherboard Most motherboards have the following components in the rear panel. • A serial port- is used for connecting old peripherals. • A parallel port- is mainly used for connecting old printers. • USB ports(1.1, low-speed, or 2.0, high-speed)- are used for connecting more recent peripherals. • RJ45 connector (called LAN or ethernet port) – is used for connecting the computer to a network. It corresponds to a network card integrated into the motherboard. • VGA connector (called SUB-D15)- is for connecting a monitor. This connector interfaces with the built-in graphics card. • Audio plugs (Line-In, Line-Out and microphone)- is for connecting sound speakers or a hi- fi system, as well as a microphone. This connector interfaces with the built-in sound card. Fig 5 Input/Output Connectors of a motherboard Characteristics There are several ways in which a motherboard can be characterized, in particular the following: • the form factor, • the chipset, • the type of processor socket used, • The input-output connectors. Motherboard form factor The term "form factor" is normally used to refer to the motherboard's geometry, dimensions, arrangement, and electrical requirements. In order to build motherboards which can be used in different brands of cases, a few standards have been developed: • AT baby/AT full format is a format used in the earliest 386 and 486 PCs. AT and Baby AT Up until recently, the AT and baby AT form factors were the most common form factor in the motherboard world. These two variants differ primarily in width: the older full AT board is 12" wide and 13’’ deep won't typically fit into the commonly used "mini" desktop or minitower cases. AT motherboard: The original AT motherboard, later known as "Full AT", is 12 inches (305 mm) wide and 13.8 inches (350 mm) deep, which means it will not fit in "mini desktop" or "minitower cases". • Introduced in 1980 by IBM. • It supports 5-1/4" full-height drive bay. • The power connectors for AT motherboards are two nearly identical 6-pin plugs and sockets. • Key board connector is fixed on the motherboard. • It was used for computers from 4004 processors to 8088. • Processor is located near by the expansion slots. Baby AT motherboard: • In 1985IBM introduced Baby AT and soon after all. • Baby AT size was 8.5" width and 13" length. • Baby AT form factor is used for computers from the 286 processors to the first Pentiums. • The power connectors are similar to AT motherboard. • It supports 3.5 half-height drive bay. • A new expansion bus i.e, micro-channel architecture was introduced in baby AT. • The Baby AT motherboard was, through 1997, the most common form factor on the market. • The Baby AT was the first PC motherboard to build in sockets for I/O ports (serial, parallel, etc.), which were cabled to connectors on the back of the case. Widely used in 386, 486 and early Pentium PCs, the Baby AT was superseded by the ATX motherboard. • Full-sized keyboard connector soldered onto the board. The serial and parallel port connectors are almost always attached using cables that go between the physical connectors mounted on the case, and pin "headers" located on the motherboard. • The AT and Baby AT form factors put the processor socket(s)/slot(s) and memory sockets at the front of the motherboard. ATX motherboard: • In 1995, Intel introduced ATX, a form factor which gradually replaced older Baby AT motherboards. • This format was replaced by the ATX format, which shape allowed for better air circulation and made it easier to access the components. • The ATX format is an upgrade to Baby-AT. • ATX standard: The ATX standard format is traditionally 305x244 mm. It includes an AGP connector and 6 PCI connectors. • It has only one power connector which is 20 pin and known as P1. • The ATX was the first PC motherboard to not only include I/O support (serial, parallel, mouse, etc.), but to place all the connectors directly on the motherboard. Prior to the ATX, only the keyboard connector was attached to the motherboard. • The motherboard glues all the components of a computer system together via its various slots, connectors and ports. In this case, Socket A is for an AMD Athlon XP CPU. DDR slots hold SDRAM memory modules, and the AGP and PCI slots hold the adapter cards. The back panel ports stick through the back of the case o micro-ATX: The microATX format is an upgrade to ATX, which has the same primary advantages in a smaller format (244x244 mm), with a lower cost. Micro-ATX includes an AGP connector and 3 PCI connectors. o Flex-ATX: FlexATX is an expansion of microATX which offers manufacturers greater flexibility when designing their computers. It includes an AGP connector and 2 PCI connectors. o mini-ATX: miniATX is a compact alternative to the format microATX (284x208 mm), and includes an AGP connector and 4 PCI connectors instead of 3 that come with microATX. It is mainly intended for mini-PCs (barebone computers). BTX motherboard: • The BTX format (Balanced Technology eXtended), supported by Intel, is a format designed to improve upon the arrangement of components, so as to optimize air circulation, acoustics, and heat dissipation. • This new format will substitute the current ATX standard in the next few years. • The new format was launched for two basic reasons: first, to improve the thermal dissipation of the computer (that is, its internal ventilation). With processors that have higher and higher clock speeds, and with other components, such as video cards, memories, and hard disks, generating more and more heat in the computer, it is natural to think about a better way to refrigerate the PC.