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The Basic Input/Output System
Unit objectives:
 Access the BIOS setup utility, change
hardware configuration values, and
research BIOS updates
 Explain the POST and boot
processes; and identify the symptoms
of, probable causes of, and potential
solutions to problems with the BIOS
and POST
Topic A
 Topic A: The BIOS and CMOS
 Topic B: The POST and boot
processes
Firmware
 Gray area between hardware and
software
 Software written permanently or semipermanently to a computer chip
 Used to control electronic devices
 Implemented in PC with BIOS and
CMOS
BIOS
 Basic Input/Output System
 A set of software instructions stored
on a chip on the motherboard
 Enables basic computer functions
 Common BIOS manufacturers:
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AMI
AWARD
MR BIOS
PHOENIX
 Many use shadowing
CMOS
 Area of memory that stores BIOS
configuration information
 Battery provides power to CMOS
 Type of computer chip:
complementary metal oxide
semiconductor
 Can maintain information when
system’s power is removed
CMOS battery
Battery
CMOS configuration
 Configure with system setup utility
– Built in BIOS
 Access to utility varies by
manufacturer
BIOS configurable settings
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Date and time
Boot sequence
CPU options
Optical drive options
Floppy drive options
Hard drive options
Serial port options
Parallel port options
Integrated devices
continued
BIOS settings, continued
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Performance features
Plug and Play
Power management options
Security
Virus detection
Activity A-1
Updating your PC’s BIOS settings
BIOS updates
 BIOS implemented either in:
– ROM: Programmed at factory (older technology)
– Flash memory: Can update, “flash,” the BIOS
 Update if you:
– Have device problems or other bugs that PC
manufacturer says are caused by BIOS
problems
– Have device problems that can’t be attributed to
anything else;
have exhausted all other troubleshooting
avenues
– Need to use new hardware options that are
supported by system but not by BIOS
BIOS update sources
 Links to BIOS updates and flashing
utilities on PC manufacturer’s Web site
 BIOS is tailored by each PC
manufacturer
 Don’t go to BIOS manufacturer’s Web
site
Determining the BIOS version
1. Open System Information (or DxDiag)
2. Record BIOS Version/Date field value
3. If present, record SMBIOS field value
Flashing the BIOS
1. Determine current BIOS version
2. Go to PC manufacturer’s Web support
pages
3. Compare available updates with current
version
4. Download new BIOS version
5. Download flashing utility
6. Close all open windows
7. Open flashing utility; follow instructions
8. Restart PC
BIOS update guidelines
 Don’t update your BIOS unless you
must
 Never turn off your computer during a
BIOS update
– Connect desktops to a UPS
 Use the correct BIOS flash utility
 Follow instructions exactly
 Back up BIOS if possible
Recovering from a failed update
 Use BIOS backup to restore previous
version
 Use “boot block”
 Use flash recovery jumper switch
 Obtain new BIOS chip
Activity A-2
Researching BIOS updates for your PC
Bad CMOS battery
 BIOS data retained due to CMOS
battery
 Older PCs had a soldered battery—
not easily replaceable
 Newer PCs have removable battery
 Typically a button cell battery
 Charge generally remains long
enough for replacement
Low battery errors
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Loss of time or date at boot
CMOS Read Error
CMOS checksum error
CMOS Battery Failure
Replacing the CMOS battery
1.
2.
3.
4.
5.
Record custom CMOS setting values
Power down; open your computer’s chassis
If necessary, remove cables to allow battery access
Gently slide the battery out of its compartment
If necessary, discharge the CMOS memory using
motherboard jumpers
6. Insert the new battery into the holder
7. Reconnect any cables you disconnected to gain
access to the battery
8. Close the PCs chassis
9. Reconnect any cables and power cord
10. Reboot. Enter correct date and time
11. Access BIOS to reset custom values
Activity A-3
Replacing the CMOS battery
Topic B
 Topic A: The BIOS and CMOS
 Topic B: The POST and boot
processes
POST process
 Power-on self test
1. BIOS tests core hardware
2. BIOS tests video subsystem
3. BIOS identifies itself, including its:
 Version
 Manufacturer
 Date
4. BIOS tests main system memory
Beep codes
 Inform user of errors before display is
loaded
– System speaker must be functional
 Vary by manufacturer
 www.computerhope.com/beep.htm
 Common beep codes:
– 1 short beep = No problems found
– 3 long beeps = Keyboard error
– 8 short beeps = Video adapter memory
problems
– 9 short beeps = BIOS problem
– 1 long + 3 short beeps = Memory error
Numeric codes
 Informs user of errors after display is
loaded
 Vary by manufacturer
 Lenovo numeric code examples:
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151 = Real time clock failure
161 = Bad CMOS battery
162 = Configuration mismatch
164 = Memory size mismatch
201 or any 20# = Memory failure
1762 = Hard drive configuration error
Activity B-1
Observing the POST process
The boot process
1. You turn on the power
2. Timer chip sends reset signals to CPU to
prevent booting
3. Power supply performs internal checks;
sends Power_Good signal to CPU
4. Timer stops sending reset signals to CPU
5. CPU loads BIOS and BIOS extensions
6. BIOS checks whether this is a cold or warm
boot
continued
The boot process, continued
7. If cold boot, BIOS performs POST
8. BIOS reads CMOS and configures devices
9. Plug and Play devices detected and
configured
10. BIOS determines which drive to boot from
11. BIOS reads the master boot record from
drive
12. OS takes over and completes the boot
process
Boot devices
 Used to load operating system
 Current:
– Internal hard disk
– Optical drive: CD or DVD
– USB drive: flash drive or external hard disk or
optical drive
– Network drive, using a PXE network interface
card
 Older:
– Floppy disk drive
– SCSI device
– Zip drive
Boot devices in the system BIOS
Activity B-2
Checking the boot order
BIOS-related problems
 Devices misidentified
 Wrong memory size reported during
POST or available during booting
 Hard drive inaccessible
 System won’t boot from hard drive
 System boots from the wrong device
 Date and time incorrect or reset after
computer is turned off
POST-related problems
 There’s no video; instead, the
computer sounds 8 short beeps
 The system emits 3 long beeps
 The system emits 1 long and 3 short
beeps
 POST code 162 is displayed
 POST code 164 is displayed
CMOS-related problems
Error messages:
 Non-system disk or disk error
 Display type mismatch
 Memory size mismatch
 CMOS checksum failure
Activity B-3
Troubleshooting BIOS and
POST problems
Unit summary
 Accessed the BIOS setup utility,
changed hardware configuration
values, and researched BIOS updates
 Explained the POST and boot
processes; and identified the
symptoms of, probable causes of, and
potential solutions to problems with
the BIOS and POST