MELJUN CORTES Computer Organization Lecture Chapter5 BIOS CMOS

8/10/2019 MELJUN CORTES Computer Organization Lecture Chapter5 BIOS CMOS

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Chapter 5

BIOS and CMO

MELJUN CORTES


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We Need to Talk

Historical/Conceptual


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

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 that connectthe CPU to video and/or

memory

Southbridge

Handles all of the inputs andoutputs to the many devices

in the PC

A chipsetis a set of Northbridge andSouthbridge chips that work together

Explored in more depth in Chapter 7


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Data Flow Northbridge and Southbridge

have connectivity with all devices

Not the same in all systems


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

Chipset

Northbridge

Southbridge



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 to enable theCPU to talk to other devices

A Flash ROM chip stores these programs

These programs are collectively known as thebasic 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



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


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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



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 todays PCs



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 all the new

types of hardware

Ways to bring your own BIOS(BYOB) wereinvented:

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

Most new hardware devices use device driversto

tell the BIOS how to talk to the CPU

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


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Device Drivers

A device driveris a file that contains the BIOScommands necessary to communicate with the

devices they support

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 CPU tocommunicate 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 a specialprogram stored on the ROM chip

Initiated when the computer is turned on or is reset

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 found in legacy

computers

Check motherboard manual for meaning


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Text-Based Error Message


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POST Cards

POST cardsare devices that monitor POSTs and reporton the hardware that may be causing problems

Turn the PC off, plug in the card,

and reboot

POST error codes do not fix the

computerthey just tell you

where to look

If all else fails, replace the

motherboard


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The Boot Process

The CPU is the first component initialized whenthe computer is turned on

It reads a special wire called power goodonce

the power supply provides the proper voltage to

the CPU

Every CPU has a built-in memory address withthe 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 thebootstrap 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


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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 the shunt onthe 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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Documents

MELJUN CORTES Computer Organization Lecture Chapter5 BIOS CMOS