1. Basic Input Output System
BIOS
Basic Input Output System

2. How does a computer get started?
WAKE UP!

3. 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

4. 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

5. 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

6. BIOS in ROM Bootstrap Program non-volatile BIOS Data On a separate
chip on MB.
Always there.
BIOS utilities
video, hard drive i/o etc
volatile
RAM
Memory you
install

7. 1. Start running bootstrap
Bootstrap Program
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

8. 1. Start running bootstrap
Bootstrap Program
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

9. 1. Start running bootstrap
Bootstrap Program
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

10. 1. Start Running Boostrap
Bootstrap Program
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

11. 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

12. 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.

13. 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

14. 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.

15. Summary BIOS has 3 main parts
Bootstrap
Configuration data
I/O routines
Main concern for you is updating configuration data