© 2007 the mcgraw-hill companies, inc. all rights reserved bios and cmos chapter 5

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

BIOS and CMOSChapter 5


Overview

• In this chapter, you will learn to

– Explain the function of BIOS

– Distinguish among various CMOS setup utility options

– Describe option ROM and device drivers

– Troubleshoot the power-on self test (POST)


We Need to Talk

Historical/Conceptual


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


Northbridge & Southbridge

• Northbridge– Chip or chips that

connect the CPU to video and/or memory

• Southbridge– Handles all of the inputs

and outputs to the many devices in the PC

• A chipset is a set of Northbridge and Southbridge chips that work together

• Explored in more depth in Chapter 7


Data Flow

– Northbridge and Southbridgehave connectivity with all devices

– Not the same in all systems


Chipset

Northbridge

Southbridge


Basic Input/Output System (BIOS)

• Bridges connect the devices– But without a program, they don’t know how

to communicate

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

• A Flash ROM chip stores these programs

• These programs are collectively known as the basic input/output service (BIOS)


Talking to the Keyboard

• The keyboard talks to the external data bus – Uses the keyboard controller chip (8042)


BIOS

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

known as firmware• Programs stored on erasable media are

called softwareKeyboard controller

chip


CMOS

Essentials

CompTIA A+Essentials


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


BIOS vs. CMOS

• BIOS– Programs

– Non-volatile (stays same after power off)

– Can be changed by “flashing”

– Typically 64 K of programs (though Flash ROM is much bigger)

– Often a separate chip

• CMOS– Data

– Volatile (kept alive with battery)

– Changed via CMOS setup

– Typically 128 K of data (though chip size is typically 64 K)

– Often on Southbridge


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)


CMOS Setup

• Main menu – Access to all submenus


Standard CMOS Features

• Clock, hard drives, floppy drives


SoftMenu Setup

• Normally set to Default or Auto for all


Advanced Features

• POST, boot order


Power Management

• Use to enable/disable power-saving features


PnP/PCI

• Rarely need to manipulate on today’s PCs


Set Password

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


Option ROM and Device Drivers


BYOB

• Computer makers could not predict all the new types of hardware

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

– Option ROM is a BIOS chip embedded on the adapter 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 for internal needs (internal function) and use a device driver to talk to the CPU


Device Drivers

• A device driver is a file that contains the BIOS commands necessary to communicate with the devices they support– Loaded into RAM when the system boots

• All devices come with their own device drivers


BIOS, BIOS, Everywhere

• All hardware needs a program to allow CPU 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


Power-On Self Test (POST)

CompTIA A+Technician

IT Technician


Power-On Self Test (POST)

• The power-on self test (POST) is a special program stored on the ROM chip

– Initiated when the computer is turned on or is reset

– Checks out the system every time the computer boots

• Communicates errors

– Beep codes

– Text errors


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 found in legacy computers– Check motherboard manual for meaning


Text-Based Error Message


POST Cards

• POST cards are devices that monitor POSTs and report on the hardware that may be causing problems

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

– POST error codes do not fix the computer – they just tell you where to look

– If all else fails, replace the motherboard


The Boot Process

• The CPU is the first component initialized when the computer is turned on

• It reads a special wire called power good once the power supply provides the proper voltage to the CPU

• Every CPU has a built-in memory address with the first line of the POST program on the system ROM


The Boot Process

• The last BIOS function called by POST is the 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 error if it cannot find the boot sector on the bootable disk


Care and Feeding of CMOS/BIOS

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


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


Losing CMOS Settings

• If your system keeps resetting

– Replace the battery

• Common symptoms of low battery

– Slow running clock

– Clock resetting to January 1st


Clearing CMOS Settings

• To clear the CMOS settings, place the shunt on the CMOS jumper

– Resets to factory settings

– Resets password


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

© 2007 the mcgraw-hill companies, inc. all rights reserved bios and cmos chapter 5

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