Motherboards

the motherboard is the central sub-assembly or the main circuit board inside a computer. It consist of a flat printed-circuit board on which is mounted a variety of chips and a few other components. The motherboard contains the central processing unit, which support circuitry of the socket for the CPU, the coprocessor, the BIOS chip, several rows of memory chips and expansion slots (AGP, PCI) and other components. It hosts the largest single collection of chips of any PC component and serves as the "street system" for the grid of wires that link all the components, making it possible for them to communicate.

The Motherboard

The motherboard (one is shown below) defines the computer's limits of speed, memory, and expandability. A computer needs more than just a CPU and memory. To accept input from the user, it needs devices, such as a keyboard and a mouse. It also needs output devices, such as monitors and sound cards, to cope with the powerful graphics and sound capabilities of the programs available today. A computer also needs "permanent" storage devices, such as floppy disk drives and hard disk drives, to store data when it is turned off. It is the function of the motherboard to provide the connectivity for all these devices, as well as for the CPU, RAM, and support integrated circuit

The motherboard is usually the largest circuit board found inside the computer case. Motherboards come in a variety of shapes. One size does not fit all, and careful attention to size and location of mounting holes is required before installing a new motherboard in an older computer. A motherboard needs to fit in the space allotted for it, be secure in its mounts, be properly grounded, receive sufficient ventilation (for cooling of the CPU and other heat-sensitive components), and must not conflict with other hardware. When considering to purchase of a new motherboard, keep these things in mind:

• Most "generic" motherboards will fit into "generic" computers. One reason some people consider purchasing a PC clone is that it is easier to upgrade. Keep in mind that a hybrid PC (assembled by a small vendor, made from untested components) may be constructed of parts that may or may not be totally compatible. There may also be questions about EMI due to interaction between components or the way the parts set in the case.
• There are two major categories of motherboards: AT and ATX. The main difference between them is the type of power supply and main power switch each requires. When you order a new motherboard, be sure to first verify that it is compatible with the case and power supply to be used.

• If you are working on a brand-name computer, you might be required to purchase a new motherboard or other custom components from the same manufacturer.
• Before buying a motherboard, check its technical references to be sure that the new board will fit and will be compatible with any of the RAM and expansion cards the owner intends to use. Often, this information can be found in the owner's manual. If not, check the manufacturer's Web site, if one is available, or check other online resources such as technical libraries. A Web search using the keyword "motherboard" will yield sites dedicated to computer hardware.
• For all practical purposes, you cannot repair motherboards. They should be replaced if physically or electrically damaged. Your customer will get new technology, usually for a price lower than the cost of the repair.
• Because it is often the most difficult part of a system to replace (you have to remove all the equipment that is connected to it), check all other internal and external components before removing or replacing the motherboard.
• When obtaining a replacement, be sure to factor in the cost of all critical options found on the existing motherboard. Some have a built-in SCSI (Small Computer System Interface) Host Adapter or display adapters that might not be common. In that case, either makes sure the new board offers the same level of support or install the appropriate add-on card(s) to bring the system up to the existing level of operation

Parts of Motherboard

* ROM chip - The chip or IC which contains and stores critical programs such as the program that boots the computer and BIOS.

* FDD Connector/Socket - A socket for Floppy Disk Drive cable connector or interface.

* Southbridge - is the chip that controls all of the computers I/O functions, such as USB, audio, serial, the system BIOS, the ISA bus, the interrupt controller and the IDE channels. In other words, all of the functions of a processor except memory, PCI and AGP. They do not normally come with a heat sink.

* Northbridge - a Chip that connects to a CPU to memory, the PCI bus, Level 2 cache and AGP activities. The Northbridge chips communicate with the CPU through the FSB.

* System Panel Connector - This connector accommodates several front panel functions a. System Power LED b. HDD Activity c. ATX Power Switch d. Reset Switch AGP Slot - Accelerated Graphics Port supports 1.5 V - Slot refers to a unit of space in a motherboard that supports AGP cards and it yields a throughput rate of 266 MBps.

* IDE Connector Socket (Intelligent Drive Electronics or Integrated Drive Electronics)

- A socket for IDE Cable connector/interface

* ATX Power Connector Socket - A socket for the ATX Power Supply Cable Connector

* Microprocessor Socket - is the connector that interfaces between a computer's motherboard and the processor itself. Most CPU sockets and processors in use today are built around the pin grid array (PGA) architecture, in which the pins on the underside of the processor are inserted into the socket, usually with zero insertion force (ZIF) to aid installation.

* Expansion Slot (PCI or ISA) - A socket on the motherboard that accepts an expansion card. * PCI – Peripheral Component Interconnect is a high-speed connection for devices including modems, sound cards, LAN cards etc. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps. PGA - A feature of a CPU socket whereby the pins are aligned in uniform rows around the socket.

* Memory Slots - A space for place the memory modules

* CMOS Battery - CMOS & Clock Backup batteries perform the same function in desktop and laptop computers: when the computer is turned off, the battery maintains the time and date, thus insuring their accuracy when the system is once again restarted. More importantly, the battery saves the computers BIOS setup configuration, which allows the system to efficiently reboot once it is restarted. The CMOS chip requires a small trickle voltage from a battery to keep its memory alive. When the battery gets low or dies, the computer will experience a sudden memory loss and thus lose settings. It might not be able to find the floppy disk or first hard disk drive and therefore display an error indicating that it cannot find the system or none system disk. The voltage of CMOS batteries ranges from 3 to 6 volts. Check the motherboard or the motherboard documentation to determine the actual battery requirements. Batteries come as either on-board (NiCad batteries, soldered in place or in a fixture, that last from five to seven years) or external (none rechargeable AA alkaline batteries that last from two to four years). The 3-volt lithium watch battery is becoming very popular with motherboard suppliers. Many of these are mounted in a special holder so that the battery can be easily changed; however, some manufacturers solder them in place.

Important sections of motherboard

1) Processor socket - This is the socket on the motherboard where processor is mounted. There are basically 3 types of slots. Socket 370 (for Via), Socket A and Socket 478 (For Pentium4 processor).

2) Chipset - A motherboard comes with a variety of support chips soldered in place. The primary elements constitute the Chipset is commonly used to refer to the core logic of motherboard designed to work with the CPU. Motherboard is built around a chipset that supports a specific class of processors and type of memory. Main system chipset is responsible for the communication between the processor, memory and other integrated components. Chipset acts a hub controlling the transfer of data between processor, its cache, system buses and peripherals. The timely transfer of data without errors is the most important function of the chipset. This function of the chipset decides overall performance of the system. That is why the maximum speed of a processor that the chipset supports is very important. For your future upgrades you will need to change only the processor. For example, if chipset supports up to 2.8GHz CPU's and you decide to buy 2 GHz, you could upgrade to a 2.8 GHz CPU with out having to invest in new motherboard. When replacing a CPU, you must make sure that it is compatible with the chip set and supported by the motherboard. If not, the computer won't work. A basic chip set consists of a · Bus controller · Memory controller · Data and address buffer · Peripheral controller

On modern motherboards, you will find specialized chips to control things such as cache memory and high-speed buses. You will also find boards with fewer individual chips because the manufacturer has incorporated several functions into one chip. Keep in mind that there is a wide range of features (with attendant cost increases for extras) available when selecting a motherboard. You will need to keep up to date on the types of processors, memory design, CPUs, and expansion slots available to recommend and obtain the right product for your customers. Be careful in choosing motherboards with components like display adapters and sound cards on board. These are components that may not have all the features of their expansion card versions, and customers may decide to upgrade, leaving them with motherboard-based elements that could cause conflicts.

Different chipsets are used to support functions that are offered by the board - the RAM and the Processor. For example, the Intel 845 chipset supports Pentium 4 and DDR SDRAM. AMD processors (Duron and Athlon) require VIA KT 333 or 400 chipset based motherboards.

3) Interface slots - Now a days, there are basically 2 types of slots are available for ADD on cards on the motherboard - PCI and AGP. PCI slots are used for adding Ethernet card, Sound card, Modem card etc. AGP slot is used to add graphic card.

• PCI Bus (Peripheral Component Interconnect) It is 32-bit bus width, 33.33 MHz clock with synchronous transfers. The standard speed of PCI Bus is half of External Bus of CPU, for example, bus for CPU 66 MHz PCI Bus is 66/2 = 33 MHz and bus of CPU is 100 and 133 MHz, PCI speed is 100/3 and 133/4.
• AGP (Accelerated Graphic Port) as well. It is the slot designed for attaching a graphics card with maximum data rate. In a main-board, there will be one slot. AGP is 32-bit channel operating at 66 MHz resulting in a maximum data rate of 133 and 266 MHz.
• ISA - Industry Standard Architecture. Used when the original 8088 8bit microprocessor based personal computers were produced.

4) RAM slots- DDR RAM is the most popular option today. Most motherboards have at least two slots. But expensive motherboards have 4 slots. The total amount RAM you can install is also dependent on the motherboard chipset.

5) BIOS - Every motherboard has special software in ROM (Read only Memory) known as BIOS (Basic Input Output System). The jumperless motherboards that are norm today, allow for automatic parameter detection and configuration. For example - Processor core voltage and clock multiplier. Also the configuration and control of integrated peripherals are all auto-detected. The BIOS is the critical part which determines software compatibility. The BIOS is contained in one chip. The BIOS is actually the program within a chip called an EPROM (Erasable Programmable Read Only Memory). The EPROM contents can be erased using violet light and it is possible to recopy a new program onto it. The program in the BIOS controls the operation of the computer and peripherals.

NOTE: For more information and clarification with regard on this topics, feel free to read “A+ Certification Training Kit / Microsoft Corporation.--3rd Ed.” PUBLISHED BYMicrosoft PressA Division of Microsoft CorporationOne Microsoft WayRedmond, Washington 98052-6399 Copyright © 2001 by Microsoft Corporation