Cmos And Bios.ppt 253i53

BIOS and CMOS

OBJECTIVES:  In this lesson, 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)

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Bridge Introduction  Data flows through the computer  Between U and RAM  Between U and video  Between U and other devices  Bridges are used to connect the pieces  Northbridge 



Bridge closest to the U

Southbridge 

The farther bridge

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

Chip or chips that connect the U to video and/or memory

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 Southbridge 

Handles all of the inputs and outputs to the many devices in the PC

Data Flow 



Northbridge and Southbridge have connectivity with all devices Not the same in all systems

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Chipset

Northbridge

Southbridge

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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 U to talk to other devices

 A Flash ROM chip stores these programs  These programs are collectively known as the

basic input/output service (BIOS)

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Talking to the Keyboard  The keyboard talks to the external data bus 

Uses the keyboard controller chip (8042)

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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 Keyboard controller chip

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Essentials

CMOS

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

 CMOS



Programs



Data



Non-volatile (stays same after power off)



Volatile (kept alive with battery)



Can be changed by “flashing”



Changed via CMOS setup



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



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



Often a separate chip



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)

CMOS Setup • Main menu – Access to all submenus

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Standard CMOS Features • Clock, hard drives, floppy drives

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Soft Menu 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-saving features

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PnP/PCI  Rarely need to manipulate on today’s PCs

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

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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 U



Most devices with onboard BIOS use it only for internal needs (internal function) and use a device driver to talk to the U

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Device Drivers  A device driver is a file that contains the BIOS

commands necessary to communicate with the devices they 

Loaded into RAM when the system boots

 All devices come with their own device drivers

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BIOS, BIOS, Everywhere  All hardware needs a program to allow U 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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IT Technician

Power-On Self Test (POST)

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

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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 found in 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 POSTs and report

on the hardware that may be causing problems 

Turn the PC off, plug in the card, reboot



POST error codes do not fix the just tell you



If all else fails, replace the

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and

computer – they where to look

motherboard

The Boot Process  The U 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 U  Every U has a built-in memory address with the

first line of the POST program on the system ROM

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

Care and Feeding of CMOS/BIOS

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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Loosing 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 the shunt on the

CMOS jumper 

Resets to factory settings



Resets

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Flashing ROM  Flash ROM chips can be reprogrammed  program from manufacturer  Copy program to floppy  Some programs will run within Windows  Boot to floppy and run program

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Thank You

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