INTRODUCTION
The BIOS (an acronym for
Basic Input Output System)
software has a number of
different roles, but its most
important role is to load the
operating system.
BIOS is sometimes called
firmware because it is an
integral part of the system
hardware.
About BIOS
The BIOS is the default control for the
most important functions of PC.
It defines the compatibility of our PC with
expansion hardware.
Without it our PC couldn’t even boot.
HISTORY
 Before 1990 or so BIOSes were held on ROM
chips.
 BIOS firmware stored on EEPROM or flash
memory devices.
 To avoid BIOS corruption, some new
motherboards have a backup BIOS ("Dual
BIOS" boards).
 Hardware manufacturers frequently issue BIOS
updates to upgrade their products and remove
bugs.
WHAT BIOS DOES?
A power-on self-test (POST) for all of the different
hardware components in the system to make sure
everything is working properly.
Activating other BIOS chips on different cards installed
in the computer - For example, SCSI and graphics
cards often have their own BIOS chips.
Providing a set of low-level routines that the operating
system uses to interface to different hardware devices
- It is these routines that give the BIOS its name. They
manage things like the Keyboard, the Screen, and the
Serial and Parallel ports, especially when the
computer is booting.
Managing a collection of settings for the hard disks,
clock, etc.
POST
1. The first step of POST is the testing of the
Power Supply to ensure that it is turned on and
that it releases its reset signal.
2. CPU must exit the reset status mode and
thereafter be able to execute instructions.
3. BIOS checksum must be valid, meaning that it
must be readable.
4. CMOS checksum must be valid, meaning that
it must be readable.
POST(CONT…)
5. CPU must be able to read all forms of memory
such as the memory controller, memory bus,
and memory module.
6. The first 64KB of memory must be operational
and have the capability to be read and written
to and from, and capable of containing the
POST code.
7. I/O bus / controller must be accessible
ACCESSING BIOS
 Keys used to access the BIOS are "Esc," "Del,"
"F1," "F2," "Ctrl-Esc" or "Ctrl-Alt-Esc" key.
 Power on the computer system and press the
key to enter the BIOS after the beep for a clean
POST is signaled.
 If the procedure has been done correctly, the
BIOS screen should be displayed rather than the
typical boot screen.
Common Options Includes :



System Time/Date
Boot Sequence
Plug and Play
Mouse/Keyboard
Drive Configuration
 Memory Security
 Power Management
Exit
What Happens when System Boots??
 The BIOS reads sector 0 (known as the MBR the Master Boot Record) from the first disk (or
from floppy or CDROM), and jumps to the code
found there - usually some bootstrap loader.
 A bootstrap loader or bootstrapping or boot
loader, is a program that resides in the
computers EPROM,PROM, or other NonVolatile Memory that automatically executed by
the processor when the computer is turned on.
EPROM
PROM
BOOT SEQUENCE







Check the CMOS Setup for custom settings
Load the interrupt handlers and device drivers
Initialize registers and power management
Perform the power-on self-test (POST)
Display system settings
Determine which devices are bootable
Initiate the bootstrap sequence
CMOS
 CMOS an acronym of
Complementary
Metal-Oxide
Semiconductor is an
on-board
semiconductor chip
powered by a CMOS
battery inside
computers that stores
information such as
the system time and
system settings.
Types of CMOS batteries
Batteries used are –
• External Lithium
• Coin Cell
• Barrel Style Solder
• PS2 6v
Life Time of a CMOS
battery - Standard
lifetime of a CMOS
battery is around 10
Years.
Flash memory
A form of non-volatile memory that can be
electrically erased
Reprogrammable
Flash memory is used for easy and fast
information storage
It is erased and programmed in blocks
consisting of multiple locations .
Less costlier.
TYPES OF BOOTING
COLD BOOT
WARM BOOT
BIOS Boot Devices
 A Boot Device is any device that must be
initialized prior to loading the operating system.
This includes :
 primary input devices (keyboard).
 primary output device (display).
 Initial program load device (floppy drive, hard
drive, CD-ROM,USB flash drive, etc).
OVERCLOKING
Process of forcing a computer component to run
at a higher clock rate than designed or
designated by the manufacturer.
Boost a computer system's performance by
increasing clock frequencies
Advanced Configuration and Power
Interface
The Advanced Configuration and Power
Interface (ACPI) specification is an open
industry standard first released in December
1996 developed by HP, Intel, Microsoft, Phoenix
and Toshiba that defines common interfaces for
hardware recognition, motherboard and device
configuration and power management.
According to its specification[1], "ACPI is the key
element in Operating System-directed
configuration and Power Management (OSPM)".
List of BIOS suppliers:
 American Megatrends (AMI)
 Phoenix Technologies
 Award Software International (merged with
Phoenix in 1998)
 MicroID Research (MR BIOS)
 Insyde Software (Insyde)
 General Software (General Software)
The Fall and Rise of the BIOS
 Older operating systems such as DOS called on
the BIOS to carry out most input-output tasks
within the PC; with the introduction of newer
operating systems such as Microsoft Windows
and Linux, the BIOS was related to principally
providing initial hardware setup, and
bootstrapping. Once it was up and running, the
operating system didn't have to rely on the BIOS
for much.
 In recent years, however, by way of systems
such as ACPI, the BIOS has taken on more
complex functions such as aspects of power
management, hot plug, thermal management
etc. This has led to renewed reliance on the
BIOS by operating system producers, and an
increase in complexity in the BIOS code
AMI BIOS
BEEPCODES
DESTRUCTION
1 short
DRAM refresh failure
2 short
Parity circuit failure
3 short
Base 64K RAM failure
4 short
System timer failure
5 short
Process failure
6 short
Keyboard controller Gate A20 error
7 short
Virtual mode exception error
8 short
Display memory Read/Write test failure
9 short
ROM BIOS checksum failure
10 short
CMOS shutdown Read/Write error
11 short
Cache Memory error
1 long, 3 short
Conventional/Extended memory failure
1 long, 8 short
Display/Retrace test failed
AWARD BIOS BEEP CODES
Description
1 long, 2 short
Indicates a video error has occurred and the BIOS cannot
initialize the video screen to display any additional
information
Any other beep(s)
RAM problem.
IBM Beep Code
Description
No Beeps
No Power, Loose Card, or Short.
1 Short Beep
Normal POST, computer is ok.
2 Short Beep
POST error, review screen for error code.
Continuous Beep
No Power, Loose Card, or Short.
Repeating Short Beep
No Power, Loose Card, or Short.
One Long and one Short Beep
Motherboard issue.
One Long and Two Short Beeps
Video (Mono/CGA Display Circuitry) issue.
One Long and Three Short Beeps.
Video (EGA) Display Circuitry.
Three Long Beeps
Keyboard / Keyboard card error.
One Beep, Blank or Incorrect Display
Video Display Circuitry.
MACINTOSH TONES
ERROR
Error Tone. (two sets of different
tones)
Problem with logic board or SCSI bus.
Startup tone, drive spins, no video
Problem with video controller.
Powers on, no tone.
Logic board problem.
High Tone, four higher tones.
Problem with SIMM.
PHOENIX Beep Code
Description / What to Check
1-1-1-3
Verify Real Mode.
1-1-2-1
Get CPU type.
1-1-2-3
Initialize system hardware.
1-1-3-1
Initialize chipset registers with initial POST values.
1-1-3-2
Set in POST flag.
1-1-3-3
Initialize CPU registers.
1-1-4-1
Initialize cache to initial POST values.
1-1-4-3
Initialize I/O.
1-2-1-1
Initialize Power Management.
1-2-1-2
Load alternate registers with initial POST values.
1-2-1-3
Jump to UserPatch0.
1-2-2-1
Initialize keyboard controller.
1-2-2-3
BIOS ROM checksum.
1-2-3-1
8254 timer initialization.
1-2-3-3
8237 DMA controller initialization.
1-2-4-1
Reset Programmable Interrupt Controller.
1-3-1-1
Test DRAM refresh.
1-3-1-3
Test 8742 Keyboard Controller.
1-3-2-1
Set ES segment to register to 4 GB.
Top 6 Reasons To Upgrade BIOS
AGP Video
CPU Upgrading
Large Hard Drive support
Faster I/O Speeds
Windows XP ACPI 2.0 Compliance
Windows 2000 ACPI 2.0 Compliance
LINKING TO HARDWARE
 BIOS routines uses memory or I/O Ports to pass
the commands and data to Hardware Devices.
 In Memory Mapping a block of memory is used.
 In I/O mapping I/O Ports are used .
BIOS SETUP ENTRY POINTS
BIOS MAKER
ENTRY KEYS
WHEN
AMI
del
During POST
AWARD
Ctrl + Alt +Esc
Anytime
IBM
Ctrl + Alt +Ins
PHOENIX
Ctrl + Alt +Esc
After Ctrl + Alt +
Del
Anytime
FLASH BIOS
 Better than EPROM
 Can Encode the BIOS Program more quickly
into Flash ROM than EPROM.
BIOS SHORTCOMINGS
Device Drivers
Flash Laziness
BIOS Shadowing
Direct Control
BIOS Bugs
BIOS TROUBLESHOOTING
 During POST BIOS generates two types of
error messages –
•
Beep Codes.
•
POST Codes.
GENERAL SYMPTOMS
 BIOS Checksum Error – default loaded
 CMOS Memory Size Mismatch
 Data Error
 CMOS Battery Failed
 Hard Disk Failure
 BIOS ROM Checksum Error –System Halted
BIOS UPGRADE TROUBLESHOOTING
 Flash Loader Utility Refuses to Run
 Erase Chip Failure
 Flash Chip Not Supported
 System Refuses To Recognize Drives
 Cannot Print Under DOS Or Windows