MELJUN CORTES Computer Organization Lecture Chapter5 BIOS CMOS
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Transcript of 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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2007 The McGraw-Hill Companies, Inc. All rights reserved
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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2007 The McGraw-Hill Companies, Inc. All rights reserved
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 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
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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 (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)
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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-saving features
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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 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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