BIOS
Basic Input Output System
How does a computer get started?
WAKE UP!
Important things to remember
• Computers only run programs
• If there is no program, there is nothing to do
• There is an “in the beginning” problem
– How does the computer get the first program in
it’s memory
• When we turn on the computer where does
it get the first program
– From the boot partition of the hard drive … NO
So WHERE?
• From the ROM
• Read-Only-Memory
• Contains the bootstrap program
• It is where everything starts
• The first instruction of the bootstrap
program is where execution always starts
So what does it do?
• Checks basic systems like keyboard, video
and main memory (RAM memory)
• Reads some of the ROM-stored data to
determine configuration
• Does a basic system check
• Goes to the proper boot device indicated by
the ROM configuration data and tries to
load the bootloader for the appropriate OS
BIOS in ROM
Bootstrap Program
non-volatile
BIOS Data
On a separate
chip on MB. BIOS utilities
Always there. video, hard drive i/o etc
volatile
RAM
Memory you
install
Bootstrap Program 1. Start running bootstrap
BIOS Data 2. Read BIOS data to determine
machine configuration
BIOS utilities
video, hard drive i/o etc
3. Read bootloader info from
the hard drive
RAM 4. Boot OS from drive
Hard Drive
Bootstrap Program 1. Start running bootstrap
BIOS Data 2. Read BIOS data to determine
machine configuration
BIOS utilities
video, hard drive i/o etc
3. Read bootloader info from
the hard drive
RAM 4. Boot OS from drive
Hard Drive
Bootstrap Program 1. Start running bootstrap
BIOS Data 2. Read BIOS data to determine
machine configuration
BIOS utilities
video, hard drive i/o etc
3. Read bootloader info from
the hard drive
RAM 4. Boot OS from drive
Hard Drive
Bootstrap Program 1. Start Running Boostrap
BIOS Data 2. Read BIOS data to determine
machine configuration
BIOS utilities
video, hard drive i/o etc
3. Read bootloader info from
the hard drive
RAM 4. Boot OS from drive
Hard Drive
BIOS data
• You can change this data at boot time
• Usually press DEL when prompted, before
it tries to boot from the drive
• A program will allow you to alter basic
information about machine configuration
• Much of it is automated
• Some you either want to override or it can
not be determined automatically
Passwording your BIOS
• DON’T
• You might want to do that in a professional
setting to protect malicious users from
booting from floppy, etc.
• Can be reset on the motherboard.
BIOS data
• Hard drives, floppies, memory
– Usually automatic
• What drive to boot and the order to
examine
• System date/time
• Overclocking specs
• Be careful, but you can always go back to
default (initial) setups
• Remember to save changes when finished
Other BIOS procedures
• Some I/O functions complex.
• Bootstrap program needs to do things like
read the hard drive.
• Routines are embedded in BIOS to help
have basic functionality for I/O no matter
what OS you boot.
• Most OSs use there own functions once
booting is done.
Summary
• BIOS has 3 main parts
– Bootstrap
– Configuration data
– I/O routines
• Main concern for you is updating
configuration data