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. The second reason is to try to standardize the formats of small-sized motherboards, used mainly in small-sized PCs. • The BTX format has three basic sizes: pico-BTX (7.9 in. x 10.4 in. – 20.32 cm x 26.67 cm), mic-roBTX (10.3 in. x 10.4 in. – 26.41 cm x 26.67 cm) and BTX (12.7 in. x 10.4 in. – 32.51 cm x 26.67 cm). • The main difference among ATX and BTX motherboards is the position of the slots. BTX motherboards are like mirrored ATX boards. Where the connectors of the serial ports, parallel ports, keyboard, mouse, USB, etc. are soldered today we find the expansion slots in the BTX boards. And where the expansion slots are today, in BTX motherboards we find the board connectors (serial ports, parallel ports, keyboard, mouse, USB, etc.). • Another change was the distance between the motherboard and the metallic chassis of the PC case, which is now 0.4173 in. (10.6 mm), bigger than the distance in the ATX standard, which improves the flow of air in lower part of motherboard and facilitates the use of systems to fit in the cooler of larger processors. • Due to these differences, BTX motherboards cannot be installed in ATX cases; neither can ATX motherboards be installed in BTX cases. • Besides, as BTX motherboards will use PCI Express slots, they will need a new power source, because motherboards with this new type of slot need a new power source, which uses a 24-pin plug (the ATX power sources use 20-pin plugs). In other words, the current ATX sources won't fit in BTX motherboards.

ITX

The ITX format (Information Technology eXtended), supported by Via, is an extremely compact format designed for miniature configurations such as mini-PC. There are two major ITX formats

o mini-ITX, with small dimensions (170x170 mm) and a PCI slot;

• nano-ITX, with extremely small dimensions (120x120 mm) and a miniPCI slot. For this reason, the choice of the motherboard (and its form factor) depends on which case is chosen. The table below summarises the characteristics of the various form factors.

Form factor Dimensions Slots ATX 305 mm x 244 mm AGP / 6 PCI microATX 244 mm x 244 mm AGP / 3 PCI FlexATX 229 mm x 191 mm AGP / 2 PCI Mini ATX 284 mm x 208 mm AGP / 4 PCI Mini ITX 170 mm x 170 mm 1 PCI Nano ITX 120 mm x 120 mm 1 MiniPCI BTX 325 mm x 267 mm 7 microBTX 264 mm x 267 mm 4 picoBTX 203 mm x 267 mm 1

Common computer motherboard problems

1. When you turn off your computer and switch it back on again it has lost the time and date settings and has also lost its BIOS so what could it be?

Cause: The motherboard on your computer has a small battery giving it the ability to hold this small amount of information when the computer has been shut down although if this battery has gone dead it will not be able to retain this information. With older computers it tends to be a bit more difficult as the battery is usually soldered on to the board it's self, whereas with newer models they tend to have batteries similar to that in a watch.

Solution: Change the battery. When changing your battery (if possible with out a computer repair technician i.e. you have a newer computer) it is very important for you to identify the exact battery you will require before installing it onto your motherboard. It is fairly simple to replace the battery once you have identified the correct one you will need to remove the casing the battery will be clearly visible on the motherboard before touching the inside of the computer it is a wise idea to touch metal that is grounded just to prevent any static shocks (static electricity can damage sensitive parts inside your computer). Then it will be a case of unclipping the battery from its holding and replacing it with the new one. 2 How can I stop my computer from turning itself on and off and it also sometimes restarts all by itself?

Cause: If these are the symptoms your PC is showing then there is a big chance it is your motherboard causing the problems try the connections on the motherboard and all of the standoff holes are filled. If these are all fine then the problems could be due to over heating you must ensure all fan out let have adequate room for ventilation. Also causing over heating could be the wiring inside blocking the fan from working correctly, all you need to do to check this is remove the outer casing and look for the fans inside ensuring no big wires are fitted incorrectly blocking the ventilation inside your computer.

Solution: If there is a group of cables preventing the air flow then you can simply tie them together and fasten them out of the way of the fan and ventilation escapes. There are many places you can now go for more information on diagnosing problems with your motherboard yourself. Though because of the mass of problems that can actually occur with your motherboard and other parts of your PC it is always advised to seek the advice of a professional if you aren't entirely sure what the problem is.

3.One of the most common failures following motherboard or RAM upgrades is improper insertion of memory modules. The levers should be lowered before inserting the memory module, and should raise themselves up and lock in place when the module is correctly seated. If you're using obsolete RIMM (Rambus Inline Memory Module) memory, the modules in a bank must be matched, and you must install CRIMMs (Continuity RIMMs) in the empty sockets. If you're using older SIMM (Single Inline Memory Modules), each bank needs a matched pair. In both cases, matched doesn't just mean capacity and speed, it also means manufacturer. I have a new page up for upgrading laptop memory with SODIMMs. For replacing regular DIMM memory, see the illustrated replacing RAM.

4. There are a number of reasons for a system with a good power supply to refuse to power up which were covered in the power supply diagnostics. Another reason is a failed CPU insertion, whether it's a slot or socket CPU. With good lighting, using a flashlight if necessary, make sure that any socket CPU is sitting dead flat in the socket, which means that the heatsink should be perfectly parallel to the motherboard surface; the CPU may be so totally hidden beneath some heatsinks that you can't see the edges. This problem should really only be relevant if you just upgraded your CPU or installed a new motherboard, because the CPU socket locks the CPU in firmly and the heatsink adds another level of clamping. If a socket CPU is a new install, you have to remove the heatsink and CPU to visually inspect it for damage such as crushed or bent legs. A CPU will not seat correctly if the socket locking arm wasn't raised all the way up before the CPU was inserted, or wasn't lowered all the way down after. If your CPU won't sit down in the socket properly, either the socket is faulty or you have the wrong CPU for the motherboard! I haven't seen a CPU creep out of a socket due to thermal shock for over a decade.