BIOS and CMOS
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Transcript of BIOS and CMOS
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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 utility options
– 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 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
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Data Flow
– Northbridge and Southbridgehave 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 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)
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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 softwareKeyboard controller
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 today’s 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) 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
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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
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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
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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 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, and reboot
– POST error codes do not fix the computer – they 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 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
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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
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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 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, CD, or USB – Some programs will run within Windows
• Boot to floppy, CD, or USB and run program
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