module - motherboard

8/13/2019 Module - Motherboard

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Module 5 Motherboard

PC Hardware Technologies I

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Module 5

Motherboard

Lessons

Motherboard Standard Expansion Buses Choosing, Installing and Troubleshooting a Motherboard

The motherboard is considered to be the heart of any personal computer. It is a Printed CircuitBoard that performs all functions necessary for the smooth functioning of the computer. As an

entry-level IT professional, you would necessarily have to learn each and every aspect of themotherboard. You would be required to identify and understand the importance of the physical

form factors, components, CMOS settings, Power on Self Test (POST), system resources, system

chipsets and controllers of the motherboard. A strong understanding of these components andtheir working will also help you troubleshoot them as and when the situation arises.

Apart from the components of the motherboard, you will also learn another important concept

named Standard Expansion Buses. These are basically the I/O slots that are otherwise known asexpansion slots. These slots are used by peripheral devices to communicate with the processor.

The standard expansion buses or slots hold expansion cards like the sound card, VGP, AGP andnetwork card. At the workplace, you would be given the task of identifying the different slotsthat will hold different cards, identify the working and linking of each slot, and ensure that they

are in proper working condition.

Another important aspect of solving issues related to the motherboard is identifying the right

type of motherboard so as to suit your customers requirements. Also, as a PC, bench or support

technician you must troubleshoot the right motherboard component in order to avoid irrepairable

losses.


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DO YOU KNOW

1. Which of the following is not a common name for the primary printed circuit board in a PC?

A. MainboardB. Motherboard

C. Planar boardD. Systemboard

Answer: C

2. Which of the following are common motherboard form factors? (Choose three.)

A. Mother AT

B. AT

C. ATXD. Baby AT

Answer: B, C, D

3. Which of the following motherboard form factors is nearly square?

A. Mother ATB. ATC. ATXD. Baby AT

Answer: B

4. Which computer component contains the circuitry necessary for all components or devices tocommunicate with each other?

A. Motherboard

B. Adapter boardC. Hard driveD. Expansion bus

Answer: A

5. Which statement best describes the purpose of the motherboard?A. Supplies DC power to the peripheral devicesB. Interconnects the primary components of the PCC. Executes all instructions of the PC

D. Stores and processes the data of the PC

Answer: B


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Lesson 5.1 Motherboard

Topics

5.1.1 Physical Form Factors

5.1.2 Motherboard Components

5.1.3 System Chipsets and Controllers

5.1.4 CMOS Settings

5.1.5 Power On Self Test (POST)

5.1.6 System Resources

Objectives:

After completing this lesson, you will be able to:

Describe the different physical form factors of motherboard Explain about different motherboard components Explain the process of Power on Self Test Configure the CMOS settings Explain the system resources used by the peripheral devices

Introduction

Motherboard forms the most significant component of a microcomputer. It is a Printed Circuit Board(PCB) which possesses different components for various purposes. The motherboard containscomponents like the Central Processing Unit (CPU), Basic Input Output System (BIOS), memory, I/O

ports, external I/O connectors, I/O controllers, expansion slots, and chipsets. Chipset is an integrated chipwhich is used to perform various functions of multiple chips. The first introduced motherboard is a PC-XT (Personal ComputerExtended Technology) motherboard.


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5.1.1 Physical Form Factors

Form factor of the motherboard refers to the physical layout of the motherboard. It also deals with the

types and shapes of cases that are used, and the different power supplies associated with it. Motherboardscan be used using two different form factors but with the same functionalities. The various form factorsavailable are:

PC-XT AT and Baby AT ATX and Micro ATX LPX and Mini LPX NLX

Personal ComputerExtended Technology (PC-XT)

PC-XT is the first kind of motherboard introduced by IBM.. The PC-XT motherboard had socket for

placing the processor and other support chips like clock generator, interrupt controller etc were presentand separate chips. The peripheral devices were plugged into the PC-Slot (Expansion slot). The XTmotherboard is illustrated in the following figure:

AT and Baby AT

Before 1997, IBM computers used motherboards of bigger size. Then due to technological advancements,the size of the motherboard was reduced to a greater extent. AT form factor was available in old computerwhich employed 80386 as its microprocessor. AT means Advanced Technology. The main disadvantageof this form factor was the size of the board. The width of the motherboard was 12 wide. This causeddisturbances to the drive bays.

To overcome the problem created by AT Form factor, the Baby AT form factor was introduced. In the

Baby AT form factor, the width of the motherboard was reduced from 12" (inches) to 8.5" (inches). Thiseliminated the problems that were associated with overlapping on the drive bays.


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Motherboard s with Baby AT form factor were designed to accommodate the peripheral devices likekeyboard, video and mouse. These peripheral devices could be connected to a circuit board that were

inserted on the expansion slot in a motherboard. The Baby AT form factor also had some disadvantages.There were advancements in the computer memory sizes. The Baby AT form factor motherboards hadmemory sockets at the front of the motherboard. The motherboards with baby AT form factor could notaccommodate the combination of processor, heat sink and fan. Cooling in a system is greatly determined

by the AT power supply which is used to blow out the air from the chassis. In order to maintain a betterair flow across the CPU, an extra chassis fan or active heat sync was required. But AT power suppliesprovided only 12V and 5V outputs to the motherboard. CPU and the additional regulators demand 3.3V.

Occasions where other heat sink on the voltage regulators and other heat dissipation components were

used, caused disturbances to the expansion slots. Hence ATX form factor was introduced to overcomethis limitation.

ATX and Micro ATX form factorDue to advancements in technology, a more integrated form factor was designed and specific locations for

keyboard, mouse, I/O and video connectors were defined. ATX form factor was introduced in mid1990s. In ATXmotherboards, the expansion slots were placed on separate riser cards that are placed in

the motherboard. This reduces the overall size of the motherboard. Along with the size of themotherboard, the case and the power supply is also altered. Advancements and enhancements in thedesign of the ATX form factor has introduced new features like

A single 20-pin connector for the power supply A power supply for blowing the air into the case. This would increase the air flow in the case. Limited overlapping between the motherboard and the drive bays Integrated I/O port connectors soldered directly to the motherboard

Thus, ATX form factor introduced many new features which made upgrading an easy job.


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ATX Motherboards have introduced some changes in the power supply unit. The system can be turned onor off from a signal in the motherboard. This provides new features in power management. Like thenotebook computers, ATX motherboards provide software controlled shut down and power up. Unlike the

AT motherboards, in ATX motherboards a 3.3 V output voltage is also provided. The processor and the

memory can be accessed easily and the positions of the peripheral connectors have been changed. Thisenables us to use short cable and reduce the electromagnetic interference. The air circulation is increaseddrastically with the help of a side vent in the ATX power supply unit. The air is blown from the side ventdirectly across the processor and the memory modules. This provides a passive heat sink and the system

noise is reduced drastically

Micro ATX form factor was advancement to the ATX form factor and offered some benefits whichenhanced the overall system design costs by reducing the physical size of the motherboard. The size of

the motherboard was reduced by limiting the number of I/O slots which is available in the motherboard.In Micro ATX form factor, more space for I/O connectors was provided at the rear end.

Some of the the features of ATX form factors are given below

Integrated I/O Connectors Reduced Overlap Between Board and Drives User-Friendly Power Connector20 Pin Power connector Better Cooling Conditions 3.3 Volt Power for processors is directly obtained from the power supply unit Automated Controls- The system can be turned off directly by pressing certain keys in the

keyboard like the space bar or by using certain commands. For example, when the shut downcommand is given, the computer performs the shut operations and the system is switched offautomatically.

LPX and Mini-LPX

ATX form factor is the most famous and commonly used one. There are some other non standard formfactors which are termed as LPX and mini LPX. These categories are used in low profile computer caseslike the desktop model. The expansion boards run parallel to the motherboard and have the raiser cardarrangement. Hence, this arrangement reduces the space and the number of expansion slots. The LPX

motherboards generally have sound and video to be integrated on to the motherboard. This provides aspace saving product and the cost is also reduced. But it has its own disadvantages. The troubleshootingof the components in this category of motherboard is difficult because of its non standardization feature.This type of motherboard is not suitable for upgrading and offers poor cooling.


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NLX

NLX form factor was introduced by Intel in 1997. The motherboards with this form factors isadvancement to the LPX design which is designed for low profile systems. The NLX format of

motherboards is small in size with 8.8 inch width and 13 inch length. Hence this format of motherboardsis suited for low profile desktop cases

The expansion slots, power cables and peripheral connectors are placed on an edge mounted raiser card as

shown in the figure. This provides easy removal of the mother board that is placed on rails in the chassis.A Full width I/O field is employed to permit different combinations of rear panel I/O. The NLX formfactor is has some advantages like providing support for new and fast changing processor technology

5.1.2 Motherboard Components

The motherboard is an integrated circuit board with many different components like the Processors, I/Oports, chipset, memory slots, co processor etc. The major components of the motherboard areA. Processor socket or slotB. ChipsetC. Super I/O chipD. BIOSE. SIMM/DIMM socketsF. Bus slots

The motherboard can be identified by using the standards given below

The socket used to hold the microprocessor defines the type of microprocessor that can beconnected to the motherboard.

Chipset is a component present in the motherboard which connects the CPU to the othercomponents present in a computer

The Basic Input/Output System (BIOS) ROM chip which stores the system configuration andperforms the Power On Self Test (POST) (diagnostic program) to check the functioning ofdifferent components in a computer

Test Yourself

1. List the different form factors


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Chipset and Functions

In the earlier days the motherboards had separate chips on the motherboard to perform different functions.With the advancement in technology, the functionalities of different chips were integrated to a single chip

called the chipset. The functionalities of different chips were integrated and made one or two large chipscalled chipset. In motherboards with PCI slots a new technology called North bridge and South bridge

was introduced. If North bridge and South bridge are integrated to a single chip then there would be asingle chip called the chipset.

North Bridge is a controller chip which is used to communicate between the processor, memory the Level2 Cache memory, the PCI bus and Accelerated Graphic Port (AGP). It makes use of the Front Side Bus

(FSB) to interact with the different components. The North bridge is used to provide fast communicationbetween the various components and the processor.

The south bridge controls and manages the slower I/O components like the serial ports, USB ports and theIDE. The south bridge is connected to the PCI bus of the North bridge


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There is also another type of technology called the Intel Hub Architecture (IHA) which uses two chipscalled hub controllers. The hub controllers manage the interaction between the processor and the other

components present in the system. The hub controllers are

Graphics and Memory Controller Hub (GMCH) equivalent to North Bridge and the differenceis that GMCH does not manage the PCI bus

I/O Controller Hub (ICH)Twice as fast as the south bridgeThe significant feature about the hub architecture is that it can identify the different data types that istransmitted over the bus to enhance its performance so as to support data being transmitted. The chipset ina computer system would determine the following:

The voltage provided to the processor Number of processors that can be supported The speed of the processor The different memory modules that are supported Bus speed The different expansion bus that are supported Power Management

Thus, the chipset controls the major functioning of the components present in the motherboard. Hence, itis very much essential to select the best chipset. Chipset is an integrated IC available on the motherboard

and cannot be upgraded like the flash BIOS ROM. To change the chipset ,you must change the entiremotherboard.

5.1.3 System Chipset and Controllers

The system chipset and controllers are the logic circuits that are the intelligence of the motherboard. Theycontrol data transfers between the processor, system buses, peripherals and almost everything within thecomputer. As data flow is such a crucial issue in the functioning and performance of several parts of the

computer, the chipset is one of the few components that have a major effect on the quality, feature set and


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speed of the personal computer. The two main benefits of integration are cost reduction and bettercompatibility. The simpler the design of the chip, integration, the less is the chance of a problem.

The following controllers are found on most of the motherboards:

The system chip The keyboard controller that controls the keyboard and the integrated PS/2 mouse as well The super I/O chip that manages input and output from the serial ports, parallel port, floppy disks

and in some instances, the IDE hard disks

Additional built-in controllers such as video, sound, network and SCSI controllers generally foundin expansion cards

5.1.3.1 Qualities and Functions of Chipset

The features and functions of chipset are as listed below:

Chipset processor support Chipset cache support Chipset memory support Chipset peripheral and I/O bus control Chipset power management support Chipset Processor Support

Choosing the type of processor is one of the main things to decide while making a new personalcomputer. Some of the factors that help in choosing the kind of processor are discussed below.

oSupport for Processor Class and Optimization

Generally most chipsets support one generation of processors and in particular 486 type systems, Pentiumclass system. The design of the control circuitry has to be distinctive for each of processor classes because

of the various methods they use cache, access, memory etc.

o Support for Processor SpeedThe measurement of the speed of the processor is made by considering two parameters, the memory bus

speed and the processor multiplier. Fast processors need chipset control circuitry that has the capacity tomanage them.

oSupport for Multiple Processor

Some chipsets support the capability for building motherboards with two or four processors on them. Thechipset circuitry manages the activities of the processors in order that they do not meddle with each

other.. They operate with the operating system software for sharing the load among the CPUs formaximum efficiency.


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Chipset Cache SupportThe cache stores recent memory accesses by the processor that enhances performance considerably as itworks much quicker than the system memory. The chipset features associated with the system or

secondary cache are discussed here in.

o Size of Secondary CacheThe chipset decides the amount of level 2 or secondary cache that will be supported. Recent chipsets

support cache of 256KB or 512 KB. However this has no relevance for Pentium Pro machines that havesecondary cache in the same package as the processor.

o Type of Secondary CacheThere are three major kinds of cache that are at present in use They are:

Asynchronous Synchronous burst Pipeline burst

Each of the kinds of cache needs different control circuitry and thus gets explicit support from the chipset.

o Write Policy of Secondary CacheA write-through cache implies that memory writes are passed on to memory immediately when the

processor passes out the information A write back cache implies that the processor writes the informationonly to the cache that at a later stage writes the information to memory at the apt time. Write back in mostcases is advanced than write-through.

o Cache ability of System MemoryThe features of chipset handle the maximum amount of memory the system can cache. Many chipsets canstore more memory than they can support with the secondary cache. The amount of cacheable memory isdependent on the chipset control circuitry and the amount of tag RAM on the board. It is not dependent on

the amount of the memory that the system currently holds.

Chipset Memory SupportThere are various styles and sizes of system memory (RAM) available for use. The chipset determinesseveral permissible features of the memory used on the motherboard.

o Support for Maximum MemoryThe chipset determines the maximum quantity of RAM a system can have on the motherboard. For recentsystems, this can be anyway between 64 MB and 4 GB. One thing to be considered about is that thisamount can be higher than the maximum amount of memory that can be cached.


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o DRAM TechnologyThe chipset regulates whether your motherboard can make use of FPM, EDO, BEDO, or SDRAM

memory.Altering the memory type influences its read and write process handled by the chipset. Additionally, some

chipsets are better than others with particular types of memory. A chipset can be optimized to offerquicker access to a specific kind of memory, while being less efficient at utilizing a different type.

o Support for DRAM Packaging and SizeTwo main types of memory packages are available for desktop computers, single in-line memory module(SIMM) and dual in-line memory module (DIMM). SIMM is available in 30-pin size and 72-pin sizes,and DIMM in 168-pin size. These packages vary in physical size and in the width of the memory they canoutput. The 30-pin SIMM generates 8 bits of data at a time, 72-pin SIMM 32 bits and DIMM 64 bits.

Generally 486 class machines need 32-bit wide memory and Pentium and Pentium Pro machines need 64-bit wide memory. However the chipset design has an effect on this.

o Support for Parity and Error CorrectionError correction logic is offered as part of the memory control circuits of the chipset. On recent personalcomputers, both parity and ECC functions are given by the use of parity memory; some chipsets support

ECC only. A chipset with no parity support has no capability to find out or correct memory read errors.

Chipset Peripheral and I/O Bus ControlMost recent computers use two buses:

Industry standard architecture (ISA) bus for slower peripherals and for compatibility with oldercomponents

Peripheral component interconnect (PCI) bus, which is a high-speed local bus for hard disks, videocards and other high-speed devices

The latest personal computers also make use of the new AGP port for video. The chipset manages these

buses, and transfers information to and from them and the processor and memory. The abilities of chipsetfind out what types of buses the system can support, what speed they can run at, and what extra features

they may have.

o Bus TypesThe chipset determines what type of buses the system can support. Intel terms its chipsets as PCISets and

AGPsets. Most recent personal computers support the ISA and PCI buses. However older chipsets on 486class machines, support the VESA Local Bus rather than PCI. There are even some 486-class personal

computers, which support all three buses on the same motherboard.

o Bus BridgesA bridge is networking term that refers to a piece of hardware, which connects two different networks and

transfers information from the computers on one network to those on the other, and vice-versa. In ananalogous manner, the chipset must use employ bus bridges for connecting together the different system


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bus types it controls. The most general type of bus bridges is the PCI-ISA Bridge that is used for

connecting together devices on two different buses.

o IDE/ATA Hard Disk ControllerCurrently all motherboards have integrated into them9 support system for four IDE hard disks, two oneach of two channels. Integrating this support makes sense for a number of causes, among them the factthat these drives are on the PCI bus and hence this saves on expansion slot.

o DMA Controller and DMA Mode SupportDirect Memory Access (DMA) gives a method for devices for transferring information directly to andfrom memory with no interference of the processor.

o Interrupt ControllerThe Interrupt Controller offers the way by which input-output devices request attention from the

processor for dealing with data transfers. This task is carried out by a pair of Intel 8259 interrupt

controllers.

o USB SupportUniversal Serial Bus (USB) is a new technology meant for replacing the present dedicated ports used for

keyboards and mice. It is yet not clear as to whether this standard will become well-known. Support forUSB is executed as part of the chipset.

o AGP SupportAccelerated Graphics Port (AGP) is a new bus particularly designed by Intel for connecting processors tohighspeed graphics cards, mainly ones executing 3D operations. It is not really a bus as it only supports

two devices.

o Plug and PlayPlug and Play is a specification that uses technology advancements in hardware, BIOSes and operating

systems, for enabling supported devices to have their system resource usage set automatically. To sh weproblem related to working of peripneral devices, plug and play needs support from the chipset.

Chipset Power Management SupportModern chipsets support a group of features that perform together for decreasing the amount of powerutilized by the personal computer during idle time. These initiatives came as a consequence of efforts intwo areas.

Those concerned about the power consumption of personal computers that are left running for asmuch as 90% of the time even though idle

Laptop personal computer owners attempting to get more life from a battery charge.


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Power management works through a number of BIOS settings that determine when to shut down differentparts of the computer when it becomes inactive. Generally the settings are progressive in order that youhave the choice for shutting down more parts of the personal computer as there is an increase in idle time.

There are several distinctive protocols that work together for making power management work.

o Energy StarEnergy star is a program started by Environmental Protection Agency for certifying personal computersthat are regarded as energy efficient and that incorporate power management or power use reductionfeatures. Most personal computers today are Energy star compliant, and show its unique logo on the

screen when the BIOS boots up.

o Advanced Power ManagementAdvanced Power Management (APM) is the name provided to the component in some operating systems

that operates with the BIOS for controlling the power management features of the personal computer. Forinstance, APM permits you for setting parameters in the operating system for controlling when several

power management features will be activated.

o Display Power-Management SignalingThis standard indicates a set of signals that can be sent by compliant video cards to compliant monitors

for directing them to go into power-conserving modes.

o System Management ModeSystem Management Mode (SMM) is a power-reduction standard for processors, that permits them to

decrease power consumption. It also integrates features such as suspend and resume.

o Hard Disk SpindownIDE and SCSI hard disk take in a command to spin down when directed. The savings here certainly is

quite negligible as recent hard disks consume little power.

Super I/O Controller Chip

Super I/O Controller chip is a small single chip similar to a chipset, present on the motherboard. It is usedto combine the functions of several separate chips. Integrating the functions of different chips into a

single one reduces the cost and simplifies the design of the motherboard. The Super I/O chip handles theoperations of slow speed peripherals present in a computer.

Super I/O controller handles three ports namely

Serial Port Control controls the serial ports, (UART-comm channel that gives input tocomputers)

Parallel Port Controlmanages and controls the parallel port Floppy Disk Drive Controlsupports the Floppy Disk Drive and floppy based tape drives


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Processor

The processor, is also termed as Central Processing Unit (CPU) is a Printed Circuit Board used for

performing Arithmetic and Logic Operations. The CPU present in a single chip is called theMicroprocessor. The CPU has two major components namely

Arithmetic and Logic Unit (ALU)performs Arithmetic and Logic Operations Control Unit (CU)provides the control signals for performing different operations.

Cache Memory

Cache memory is high speed storage memory made of Static RAM (SRAM). The Memory that is placed

in the memory socket is DRAM. DRAM provides slow access. SRAM provides the fast access and ismade of flip flops, but is expensive when compared to DRAM. Hence it cannot be used to store largeamount s of data. The data when accessed for the first time is accessed from RAM. Then a copy of it is

stored in cache memory. When the user tries to access the same data, the CPU then looks into the cachememory to see if it is available. If the data is available in the cache memory it is called cache hit. If the

data need by the user is not available in the cache memory, then again the CPU will have to access themain memory. To make quick access, the frequently used data is stored in cache memory. So, if the datais accessed again it is retrieved from the cache memory and not from the DRAM. There are two types of

cache memory. They are L1 or the internal cache and L2 cache or the external cache. The cache memoryinbuilt inside the processor is called L1 cache. L2 cache is an external cache and is present on the

motherboard.


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I/O Ports

Each device connected to a computer uses I/O port address. Each device connected to the PC uses 4,8, or

16 I/O port addresses. These addresses are used to perform some functions like

Sending commands to the peripheral device Receiving the status of the device whether it is idle or busy Send and receive data Configure the device for interrupts

Bus Speed

Bus is a electrical connection between different components in a motherboard. The bus is used fortransfer of address, data and control signals. The data transfer rate can be enhanced with the speed of the

bus. The bus speed is measured in terms of Megahertz (MHZ). The speed of the bus refers to the amount

of the data that can be transferred across the bus.

Some of the buses are

Front Side Bus (FSB) AGP bus Back Side Bus (BSB) Memory Bus IDE or ATA bus PCI bus

Front side Bus

The bus speed in general refers to the speed of the Front Side Bus (FSB). The FSB connects the CPU tothe North Bridge. The speed of the FSB can vary between 66 MHz and 800 MHz.


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The speed of the Front Side Bus greatly influences the computers performance since the processorinteracts with the memory controller by using FSB.

AGP Bus

The AGP bus connects the video card to the memory and the CPU. AGP bus operates at a speed of 66MHz

Back side Bus

The back side bus connects the processor to the L2 Cache. The back side bus is a part of the CPU. Thespeed of the back side bus is dependent on the speed of the processor

Memory bus

The memory bus connects the north bridge to the memory

IDE or ATA bus

The IDE/ATA bus connects the south bridge to the disk drives. The IDE/ATA bus is shown by thefollowing figure

PCI Bus

The PCI bus connects the PCI slots to the south bridge. The speed of the PCI bus is 33 MHz.


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To improve the speed of the computer it is necessary that the processor speed and the bus speed are insynchronization with each other. The performance cannot be improved when a slow processor works with

a fast bus speed

Jumpers

Jumper is a small connector which can be placed between two pins to make electrical connections. Thetwo pins appear on the circuit board and are electrically connected if the jumper is covering those pins.

DIP switch

The dual inline package (DIP) switch is a small block provided with a lever. The level alters the

state of the electrical connection. Change the position of the lever of the DIP switch is similar to

using a jumper. They are toggle switches and can be used to configure any device for a particular

application. The electrical connection can be closed or open using the jumper or a DIP switchdepending on their placement. DIP switches are advantageous than jumpers. DIP switch rarely

has loose connections and is more reliable. But jumpers are more commonly used since DIPswitches are comparatively expensive.

5.1.4 CMOS Settings

CMOS BIOS ROM

BIOS ROM (Basic Input/Output System Read Only memory), a special ROM chip is present in themotherboard which stores the basic system configuration. The BIOS ROM also performs a diagnostic

program called PowerOn Self Test (POST) which checks all the hardware components for any errors. Ifthe hardware is not proper, then the POST will indicate them in the form of error beeps or messages.

Test Yourself

1. What is the need for cache memory?2. What is a chipset?


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These error beeps and messages help the System Administrator to troubleshoot the problem easily. Thefour major components of BIOS are:

POST Boot s strap Loader CMOS Setup BIOS

POST BIOS ROM runs the POST as soon as the system is switched on. This tests the different

hardware components to make sure that they are working properly. After the POST is successful theprocess of loading the Operating system (booting) begins.

Bootstrap Loader BIOS has a program called Bootstrap loader which locates the operating system.After the POST is successful the control is transferred to Bootstrap loader.

CMOS Setup- BIOS ROM has a configuration program which helps you to configure hardware settings

and also the system settings like the computer date and time, system password etc.

BIOS ROM is a collection of drivers and is an interface between the hardware and the operating system.

For some devices like keyboard the drivers are not installed and the BIOS provides the driver support

CMOS Battery

All the motherboards have a battery present in them. This battery is used to power up the Real time ClockChip. This chip runs all the time regardless of the power supply. This chip maintains the system date andtime. It has 64 bytes of data out of which 10 bytes of data are used by the Real Time Clock chip and the

remaining 54 bytes are used for other activities. BIOS store the system configuration settings in theCMOS RAM area. The information regarding the hardware configuration settings like the number of hard

disks are stored in the CMOS RAM. Hence a battery is used to provide power supply to store theconfigured changes. If the CMOS battery fails the hardware configuration settings, date and time settingsare lost. Hence the system will not be able to function in accordance with the configurations manually

done by the user and would operate only with the default settings


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System Configuration

The BIOS should find an operating system on a hard disk or floppy disk drive to start the computer. Thefloppy disk drives and hard disk drives are very important components that must be configured in theBIOS. The BIOS will not be able to start the system if the drive types are not correctly recognized in theBIOS. You have to run the BIOS setup program to change setting each time you change majorcomponents or build a system.

Starting the Setup Program

The BIOS configuration program is stored in the BIOS chip for those computers built since late 1980s. Infew modern systems, the setup program is run from a floppy disk drive or the hard drive, for example, the

original IBM PC. By operating a series of small rocker or slide switches called DIP switches, you can

make few settings on original IBM PC and PC/XT.

After turning on the computer, within 9 few seconds ROM based programs will start by pressing one or

more keys in combination. The keystrokes will be different from one system to another. The familiar keyson current systems are the escape (Esc) key, the Delete key, the F1 key, and various combinations likeCtrl + or Alt + another specified key. The computer will display the correct key combinations during theinitial startup screen. The settings made in the BIOS setup program are stored in the nonvolatile RAM ofthe CMOS chip. These settings are often called CMOS setting.

Step-by-Step CMOS/BIOS Configuration

During the bootstrap process, press the correct key(s) to start the CMOS setup process. Otherwise run the

setup program from hard disk or floppy disk after the computer has started. The systems that were builtsince early 1990s will start with a menu screen, as illustrated in the following figure below. According tothe BIOS brand, version, and motherboard type, the menu and the contents of the screen will change.


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1. From the CMOS setup menu, select the menu point to examine or change setting.2. Choose Standard CMOS setup to begin.

3. The standard CMOS setup screen will display in the system, which enable to configure drive, date, andtime settings.

Standard CMOS Configuration

From the standard CMOS configuration screen you can set the following items,

Date Time Hard drives connected to the IDE interface Floppy disk drive types for drives A: (first floppy disk drive) and B: (second floppy disk drive)


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This is a typical standard setup screen. On this system, during the boot process (Auto setting) the harddrives can be detected. These settings are user-defined, To make selections here, press keys to movethrough the different options which include date and time. The time must be selected in the 24 hour

format, for example 2:00PM should be entered as 14:00. Change the ordinary floppy drive into defaultfloppy drive types so that it matches with current configuration.

Follow one of the methods given below to select the correct hard drive type,

Let the system to detect the hard drives during each system boot Use an auto detection feature located here or from the main menu Manually enter the correct settings

The amount of memory onboard will also be displayed on this screen. In old systems which has 386 orolder processors require, RAM amount must be entered manually. Systems using 286 processors or betterhave similar standard CMOS configuration screens. The difference will be mainly on the types of drives

and the number of drives that can be used. The system cannot boot if the drives are not defined properly.

Automatic Configuration of BIOS/CMOS Settings

Most of the versions of the AMI and Award BIOS permit you to automatically configure all the screens

except the standard setup screen with a choice of these options from the main menu:

Turbo BIOS Defaults (also referred to as Original/ Fail-Safe on some systems) Setup Defaults (also referred to as Optimal on some systems)


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The Turbo speeds up the systems memory refresh rate. The BIOS default settings are very conventionalin memory timings and other options so that you can use that to troubleshoot the system. The Setupdefaults provide better performance. These options are listed in the setup screen.

Advanced CMOS Configuration

You can adjust optional details about the computer by using advanced CMOS configuration screen. Inthis screen, you can perform the Number Lock setting, keyboard repeats speed, type of video, settings forcache memory, and other special features. This screen is included systems built since the early 1990s.

You can use this screen to enable or disable anti-virus hardware features. The Advanced CMOS

Configuration screen is also known as the BIOS Features screen. You can use this screen to adjust bootsequence and adjust memory options such as cache and parity checking.

Recommended Advanced CMOS Settings

Apart from the floppy disk drives and hard drives which are traditionally available, you can also bootyour system using a CD-ROM, ZIP, or LS-120 drives. Depending on the BIOS version, you have to pressthe ESC key, as shown in the figure .To return to the main menu, use cursor keys to move directly to

another menu screen.


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This system offers a variety of boot options. Press the help key (F1) or press the correct key to view the

setting for any CMOS configuration option.

Option Setting Reason

Shadowing Enabled The contents of the ROM are copied into

RAM. RAM provides a faster access

than ROM and this speed up theprocessing.

Boot Sequence C: (first hard disk),

A: (floppy disk drive),CD-ROM, C:, A:

If the first boot device is set to hard disk

the BIOS will first look into the hard

disk for the bootable files. If thebootable files are not present in the hard

disk then the BIOS looks for the

bootable files from the second and thethird and otherwise if the bootable files

are missing it generates an error

message.

Cache Internal Enabled Systems speed will be fast by Cachememory.

Write-Protect Boot

Sector, Virus Warning,or Antivirus Protection

Permits normal system use Though it doesnt stop viruses, it will

prevent users from accidentallyFORMATing or FDISKing the hard

disk.


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Advanced Chipset/Chipset Features Configuration

The Advanced Chipset/ Chipset Features Configuration screen, like the one shown in the figure offers

many advanced features which vary from one system to another. Well see some important and typicalfeatures of this menu:

Cache adjustment- Some Cyrix CPUs need the user to disable pipelining for proper operation Memory types, speed, and timing- Here regulate the values to match the memory installed in

the system (for example- parity, non-parity, SDRAM, EDO, and so on)

Configuration of USB ports- You have to enable the USB ports if you want to upgrade a systemto Window 98 or Window 2000. The systems with older version of Windows will not supportUSB and those systems do not have USB ports enabled.

Configuration of the AGP slot- You have to set the size of the memory aperture used to transferdata between the system and AGP port depending on the specific AGP video card installed and

select the AGP mode (1X, 2X, and 4X)

This USB (Universal Serial Bus) and AGP (Advanced Graphics Port) options are available on the ChipsetFeatures configuration screen, along with usual system and memory timing options.

Power Management Configuration

All the systems built since the middle of 1990s are designed to allow power management. You can seeEPA EnergyStar logo when you start the computer.

Power management works like this: After a user defined period of inactivity, devices like the monitor, thehard drive, or the CPU will go into different low power modes. These are:

Standby mode-If the system uses the Display Power Management Signaling, the monitor will beblank and the hard drive will be shut down.


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Suspend mode- To save more power it will turns off the CPU. The system that use suspendmode allow you to select a special shutdown option that reminds what programs and files wereopen. Enable the system bring back to the state when the power is restored.

In the modern systems, you can prevent the system from going into power saving modes or to wake up

when an activity takes place. Set these options by the device name (modem, hard drive, floppy disk drive,parallel port, serialport) or by the devices IRQ.

This system supports both ACPI Power Management (used by Window 98) and APM (used by old

version of Windows).

Pre-requisites to make power management work,

The hard drives and monitors can be powered down and powered back up without loss ofinformation

Power management is set to check network and internet devices, like modems and network cards.It will prevent the connection from being dropped

Almost all the devices installed in a system are observed for activity to prevent data loss. Thoughthe computer can be reading data from devices on IRQ 15 or saving data to devices on IRQ 15, an

activity on IRQ 15 will not wake up the system.

User should understand the work of the power managementNormal signs of power management are:

The Keyboard which looks dead for few seconds after you start typing (since the hard drive mustspin up)

When the screen remains blank, the monitor with blinking power lights or power light withdifferent color than normal


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PnP (Plug-and-Play) Configuration Screen

Plug-and-Play (PnP) configuration permits the operating system or the system BIOS to select hardware

setting for PnP-compatible cards when first installed. It can change those settings when new cards areinstalled. The systems with Windows 95 or newer versions of Windows will support PnP BIOS. All add-

on cards and other devices (like printers, monitors, modems, and so on) also support PnP configuration.

Since the PCI cards can configure themselves, the early version of the PnP configuration were introducedwith the first Pentium-based systems with PCI slots. PnP can be used with PnP-compatible ISA cards andat the same time it can be used with PCI and AGP cards. If the system is with Windows 95, 98, or 2000

set PnP operating system to Yes.

Built-In Ports/Peripherals Setup

The Built-in Ports/ Peripherals Setup screen can enable or disable ports which built in new systems. In

few systems you can also adjust advanced hard disk options like PIO mode and block mode.

You can reserve selected IRQs and DMAs for non PnP cards by changing PnP options for IRQs andDMA channels to Legacy.


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To make an internal modem to be installed as COM 2, this systems COM 2 port is disabled. Normallyyou have to disable a built-in port if the new port is conflict with the old.

Security/Passwords

You can setup two types of passwords on many systems. One is a power-on password that must beentered to allow any use of the system and a setup password that must be entered to allow access to the

BIOS/ CMOS setup. If you loose the setting records, you cannot enable the system.

If users lose their passwords, you have to remove the battery or use the clear CMOS jumper on the

motherboard to erase the CMOS record of the passwords and all other settings. Before enabling thesefeatures, first record the system information.

Saving and Recording BIOS/CMOS Settings

BIOS allow you to save the changes and reject the changes that happen accidentally. Some BIOSautomatically save changes. Before doing any changes, be sure to review the standard CMOS setup

screen and make sure the settings are acceptable before you save and exit. Record the critical BIOSsettings like drive type information and any changes from a systems default settings.

BIOS Upgrades

BIOS need to be upgraded in any computer. Upgrading the BIOS means to change the physical chip (if itisnt a flash BIOS) or to change its contents with software (if it is a flash BIOS). Nearly all the systems

built since 1995 have flash BIOS chips which can be upgraded with software. The BOISchip bridges thehardware to the operating system (the one that needs upgradation) When it is not able to support thefollowing:

Fast CPUs New BIOS options like PnP support and Y2K compatibility


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New operating systems like Windows 98 and 2000 New hardware, such as ZIP/LS-120 removable storage drives and large IDE hard drives

BIOS upgrade is the best and it should be carried out correctly. Otherwise, it will prevent the system frombeing accessed. Follow the initial steps for maximum safety,

Record the current BIOS configuration Back up important data

Flash BIOS Upgrade

Since the BIOS manufacturers do not sell BIOS upgrade, you have to first decide where to get your BIOSupgrade. For prominent brand computers, you can search in the vendors Web site and look fordownloads ortech support links. The system will list ou t the BIOS upgrades. In the case of genericsystems, contact the motherboard manufacturer. During bootup, some systems show the makers name

but some systems display 9 series of numbers, from those numbers, you can decode and get themotherboards maker.

Sometimes you have to download a separate loader program that includes both the loader and the BIOSimage. Next, you have to install the BIOS upgrade loader and BIOS image to a floppy disk. After the

completion of the installation, restart your system with the floppy disk containing the upgrade.

Incorrect CMOS Configuration

If the CMOS is corrupted, the system cant start even after BIOS upgrade or a battery replacement. You

have to re-enter the correct settings, save changes, and restart. Generally the CMOS problem will beindicated by an onscreen error message. If it is not shown in the screen, the setting might be changed by a

user. You can restart by using the BIOS Setup auto-configure options, double-check drive configurations,save changes, and restart.

Incorrect Flash BIOS or Failed Update

The system cant start until the update processis complete or if a wrong flash BIOS file is used to update10 update your BIOS. In this case you have to contact the motherboard maker for service. From areserved part of the chip you can reinstall the mini-BIOS which available in some of the BIOS. Systemswith this feature have a jumper on the motherboard called the flash recovery jumper. If the update cant

be installed, your motherboard might have jumpers that write-protects the flash BIOS. Check the manual

to see if the system has this feature. To update a BIOS on a system with a write protected jumper, followthese points,

Perform the update. Re-enable the write-protection to keep unauthorized people from changing the BIOS. Disable the write-protection

Clearing the BIOS Password

The BIOS password can be cleared by using a CMOS jumper that is present in the motherboard. TheCMOS jumper is near the CMOS battery and is shown in the figure below


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5.1.5 Power On Self Test (POST) Error codes

The main functions of BIOS during POST are given below

Check for the integrity of the BIOS code Check for the size of the system memory and verify its integrity Discover , initialize the list of all system bused and devices Identify organize and select the devices for booting. The priority of the bootable devices can be

clearly identified.

Helps to start the Operating System Displays error codes or beep sounds if there is any problem with any device

The list of error beeps are given below

Short beep - Normal POST - system is OK 2 short beeps - POST error - error code shown on screen No beep - Power supply or system board problem Continuous beep - Power supply, system board, or keyboard problem Repeating short beeps - Power supply or system board problem 1 long, 1 short beep - System board problem 1 long, 2 short beeps - Display adapter problem (MDA, CGA) 1 long, 3 short beeps - Enhanced Graphics Adapter (EGA) long beeps - 3270 keyboard card

The list of error codes are given below

100 to 199 - System board 200 to 299 - Memory 300 to 399 - Keyboard 400 to 499 - Monochrome display 500 to 599 - Color/graphics display 600 to 699 - Floppy-disk drive or adapter

Test Yourself

1. How will you configure the boot priority for different devices?

2. What is Plug and Play?


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700 to 799 - Math coprocessor 900 to 999 - Parallel printer port 1000 to 1099 - Alternate printer adapter 1100 to 1299 - Asynchronous communication device, adapter, or port 1300 to 1399 - Game port 1400 to 1499 - Color/graphics printer 1500 to 1599 - Synchronous communication device, adapter, or port 1700 to 1799 - Hard drive and/or adapter 1800 to 1899 - Expansion unit (XT) 2000 to 2199 - Bisynchronous communication adapter 2400 to 2599 - EGA system-board video (MCA) 3000 to 3199 - LAN adapter 4800 to 4999 - Internal modem 7000 to 7099 - Phoenix BIOS chips 7300 to 7399 - 3.5-inch disk drive 8900 to 8999 - MIDI adapter 11200 to 11299 - SCSI adapter 21000 to 21099 - SCSI fixed disk and controller 21500 to 21599 - SCSI CD-ROM system

5.1.6 System Resources

System Resources are components that are used required to communicate between the hardwarecomponents in a PC. They need to be configured and setup properly for different devices to communicate

between them. Proper allocation of system resources will avoid any hardware conflicts that would disturbthe working of various devices in the system. Some of the system resources that can be configuredinclude the

Interrupt Request Channels (IRQ) Channels Direct Memory Access (DMA) Channels Input/Output (I/O) port address Memory Address

IRQ

The expansion for IRQ is Interrupt Request. Different hardware devices use IRQ signal to the processor

to catch its attention. For example, whenever a key is pressed, IRQ 1 is generated. This is an indication tothe processor that a key press event has occurred and the data is ready to be sent to the CPU. In printers,whenever a printing job is completed an IRQ 7 signal (LPT 1) is generated which indicates the CPU, thecompletion of the printing process. The Interrupt Request signals generated by different devices cannot besent through the same channel and hence there are unique channels allotted for specific devices. In earlier

days, for new devices introduced to the system, the user should configure the IRQ channel manually. But

Test Yourself1. What is POST?

2. A single beep during POST indicates-


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with the advancement in technology a concept called Plug and Play emerged which permitted automaticconfiguration of system resources. There were 8 IRQ channels used previously in XT systems (before80286). In AT systems (After 80286), 16 IRQ channels were used. The two interrupt controllers were

cascaded to avoid any technical problems. The channe1 2 of the first interrupt controller is cascaded to thechannel 9 of the second interrupt controller. For example, if a Hard disk drive raises an interrupt then it

uses the second interrupt controller and uses IRQ 14. The interrupt signal is then sent to the first interruptcontroller using the IRQ 9 which is linked to IRQ 2 of the first interrupt controller. The first interruptcontroller then sends the interrupt signal to the CPU.

There are 16 IRQ channels numbered IRQ0 to IRQ 15. When an interrupt signal is generated from any of

the I/O device, the CPU suspends the current operation and a special routine transfers the control to theinterrupt vector table. Interrupt vector table stores the IRQ channel and the memory address of thecorresponding interrupt service routine. The control is now directed to the specific Interrupt ServiceRoutine IISR). The ISR of the corresponding interrupt is executed and the control is returned back to theCPU to execute the suspended program. The following snapshot shows the different IRQ channels

associated with different devices.


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IRQ Channel number Used byIRQ0 System timer

IRQ1 Keyboard

IRQ2 Cascade Controller

IRQ3 COM 2 /COM 4IRQ4 COM 1/ COM 3

IRQ5 Sound card, Parallel Port 2 LPT 2

IRQ6 Floppy

IRQ7 LPT 1

IRQ8 Real Time Clock

IRQ9 Redirected to IRQ 2

IRQ10 Available for other devices

IRQ11 SCSI, Video

IRQ12 Available

IRQ13 Coprocessor

IRQ14 Primary IDE

1RQ 15 Secondary IDE

Direct Memory Access (DMA) channels

Direct Memory Access is a technique where the data is transferred between the peripheral device and thememory without the intervention of the CPU. This increases the speed of processing. DMA channels are

used by different devices to transfer data at high speed. Devices connected to serial and parallel port donot use DMA channels where as the sound card and the SCSI adapters use the DMA channel for


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processing data. Each device should use a unique channel. For example, if the network adapter and thetape adapter are using the same DMA channel, then it not possible to used both the devices at the sametime. Hence these conflicts should be take care when configuring devices.

DMA Channels AVAILABILITY

00 Available01 Sound device

02 Standard floppy disk controller

03 Available

04 Direct memory access controller

05 Available06 Available07 AvailableI/O Port Address

I/O Port is an interface present in a PC to connect devices. It is pathway to communicate data between

components in a computer. There is large number of I/O port addresses. It is not limited in number likethe IRQ and the DMA channels. An Intel processor supports 65,535 I/O ports. Each port is identified by aunique port address. The port address ranges from 0000h to FFFFh (in hexadecimal numbers). Everydevice when connected to a system uses the available I/O port address when transmitting or receivingdata. Each device uses a separate driver program as an interface between the device and the CPU. The

drive program should be aware of the I/O address. Each device is given a range of I/O address and isavailable in the manual given for the device. The I/O address range used by the COMM port is given bythe table

I/O Port I/O AddressCOM 1 3F8-3FF

COM 2 2F8-2FFCOM 3 3E8-3EF

COM 4 2E8-2EF

LPT1 378-37F

LPT2 278- 27F

The following snapshot displays the I/O address range used by different devices


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The following figure shows the different port address and the IRQs used by the peripheral device and the

interaction with the CPU

The IRQ are signals and are initiated by the devices. The I/O address provides the pathway fortransferring the data.

Memory Addresses

Memory is a collection of chips which is placed in the motherboard. The processors store the data usedduring its operation temporarily in the memory. The storage area in the memory is divided into logical

address which usually holds the Operating System, some applications that are currently running and aspecific range of memory address is used for the devices in the system.


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Checking for Resource Availability

If you are using Windows 3.x or MS-DOS operating system, the resource settings can be verified by

using the MSD command present in the DOS directory.

For the Operating systems like Windows 95, Windows 98 or Windows ME the System Resources can bechecked by the procedure given below

Open Device Manager by right clicking on the System icon present in the Control Panel Double click on the computer which is the first object present in the Device Manager. It displays

00 -15.If any number is not present there, then it indicates that particular IRQ is free. If all the numbers

are present once or more then it indicates that all IRQs are utilized by different devices

If the Operating system used is Windows 2000 or Windows XP, then follow the step given below toidentify the resources used by the different devices

Click StartProgramsAccessoriesSystem ToolsSystem I nformation

This displays the system information for the various hardware which are connected. The followingsnapshot discusses the different IRQs used by different devices

Test Yourself1. What are the different types of system resources?2. What is the need for IRQ?


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Summary

The various form factors which are available are

o PC-XT

o AT and Baby ATo ATX and Micro ATX

o LPX and Mini LPXo NLX

The major components of the motherboard are

o Processor socket or slot

o Chipseto Super I/O chipo BIOSo SIMM/DIMM socketso Bus slots

The four major components of BIOS are

o POSTo Boot strap Loader

o CMOS Setupo BIOS

The main functions of BIOS during POST are given belowo Check for the integrity of the BIOS code

o Check for the size of the system memory and verify its integrityo Discover , initialize the list of all system bused and devices

o Identify organize and select the devices for booting. The priority of the bootable devices canbe clearly identified.

o Helps to start the Operating Systemo Displays error codes or beep sounds if there is any problem with any device

The system resources that can be configured include the

o Interrupt Request Channels (IRQ) Channels

o Direct Memory Access (DMA) Channelso Input/Output (I/O) port address

o Memory Address

module - motherboard

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