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2007 The McGraw-Hill Companies, Inc. All rights reserved

BIOS and CMOSChapter 5

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Overview

In this chapter, you will learn to

Explain the function of BIOS

Distinguish among various CMOS setup utilityoptions

Describe option ROM and device drivers

Troubleshoot the power-on self test (POST)

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We Need to Talk

Historical/Conceptual

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Bridge Introduction

Data flows through the computer Between CPU and RAM

Between CPU and video

Between CPU and other devices

Bridges are used to connect the pieces

Northbridge

Bridge closest to the CPU

Southbridge The farther bridge

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Northbridge & Southbridge

Northbridge

Chip or chips thatconnect the CPU tovideo and/or memory

Southbridge

Handles all of the inputsand outputs to themany devices in the PC

A chipset is a set of Northbridge andSouthbridge chips that work together

Explored in more depth in Chapter 7

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Data Flow

Northbridge and Southbridgehave connectivity with all devices

Not the same in all systems

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7/38 2007 The McGraw-Hill Companies, Inc. All rights reserved

Chipset

Northbridge

Southbridge

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Basic Input/Output System(BIOS)

Bridges connect the devices But without a program, they dont know how

to communicate

A special kind of program is required toenable the CPU to talk to other devices

A Flash ROM chip stores theseprograms

These programs are collectively knownas the basic input/output service(BIOS)

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BIOS

Each program is called a service Programs stored on Flash ROM chips are

known as firmware

Programs stored on erasable media are

called software Keyboardcontroller

chip

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CMOS

Essentials

CompTIA A+Essentials

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CMOS

Separate chip from ROM BIOS

Volatile (kept alive by battery)

Stores only changeable data Not programs

Acts as clock to keep data current

Customizable via SETUP program

Often on Southbridge

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BIOS vs. CMOS

BIOS Programs

Non-volatile (stayssame after power off)

Can be changed byflashing

Typically 64 K ofprograms (though FlashROM is much bigger)

Often a separate chip

CMOS Data

Volatile (kept alive withbattery)

Changed via CMOSsetup

Typically 128 K of data(though chip size istypically 64 K)

Often on Southbridge

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Updating CMOS

Updated via BIOS program Three primary BIOS brands

American Megatrends (AMI), Award, Phoenix

To enter setup, press key combination

(may be Del, ESC,F1, F2,CTRL-ALT-ESC,CTRL-ALT-INS,CTRL-ALT-Enter,

or CTRL-S)

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CMOS Setup

Main menu Access to all submenus

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Standard CMOS Features

Clock, hard drives, floppy drives

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SoftMenu Setup

Normally set to Default or Auto for all

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Advanced Features

POST, boot order

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Power Management

Use to enable/disable power-savingfeatures

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PnP/PCI

Rarely need to manipulate on todays PCs

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Set Password

Locks access to CMOS settings Prevents non-techs from changing key settings

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Option ROM and Device Drivers

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BYOB

Computer makers could not predict allthe new types of hardware

Ways to bring your own BIOS (BYOB)were invented:

Option ROM is a BIOS chip embedded on theadapter card itself (i.e., video cards)

Most new hardware devices use device drivers

to tell the BIOS how to talk to the CPU

Most devices with onboard BIOS use it only forinternal needs (internal function) and use adevice driver to talk to the CPU

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Device Drivers

A device driver is a file that contains theBIOS commands necessary tocommunicate with the devices theysupport

Loaded into RAM when the system boots

All devices come with their own devicedrivers

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BIOS, BIOS, Everywhere

All hardware needs a program to allowCPU to communicate with it

Could be on motherboard ROM

Could be on PC card ROM

Could be loaded via a driver

Could be loaded into RAM at boot

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Power-On Self Test (POST)

CompTIA A+Technician

IT Technician

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Power-On Self Test (POST)

The power-on self test (POST) is aspecial program stored on the ROM chip

Initiated when the computer is turned on or isreset

Checks out the system every time the computerboots

Communicates errors

Beep codes

Text errors

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Beep Codes

If video is determined to be missing or faulty One long beep followed by three short beeps

If everything checks out

One or two short beeps

If RAM is missing or faulty

Buzzing noise that repeats until power turned off

More complicated beep codes may be foundin legacy computers

Check motherboard manual for meaning

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Text-Based Error Message

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POST Cards

POST cards are devices that monitor POSTsand report on the hardware that may becausing problems

Turn the PC off, plug in the card,and reboot

POST error codes do not fix thecomputer they just tell you

where to look

If all else fails, replace themotherboard

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The Boot Process

The CPU is the first component initializedwhen the computer is turned on

It reads a special wire called power good

once the power supply provides theproper voltage to the CPU

Every CPU has a built-in memory addresswith the first line of the POST programon the system ROM

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The Boot Process

The last BIOS function called by POST isthe bootstrap loader

The bootstrap loader loads the operating

system from the boot sector Searches the floppy, CD-ROM, or the hard drive

Boot order set in CMOS

The bootstrap loader generates an errorif it cannot find the boot sector on thebootable disk

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Care and Feeding of CMOS/BIOS

We have met the enemy and he is us.- Pogo

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Losing CMOS Settings

Common errors CMOS configuration mismatch

CMOS date/time not set

No boot device available

CMOS battery state low

Common reasons for losing CMOS data

Jiggling the battery while doing other work

Dirt on the motherboard Electrical surges

Faulty power supplies

Chip creep

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Losing CMOS Settings

If your system keeps resetting

Replace the battery

Common symptoms of low battery

Slow running clock

Clock resetting to January 1st

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Clearing CMOS Settings

To clear the CMOS settings, place theshunt on the CMOS jumper

Resets to factory settings

Resets password

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Flashing ROM

Flash ROM chips can be reprogrammed

Download program from manufacturer

Copy program to floppy

Some programs will run within Windows

Boot to floppy and run program

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