2. What is BIOS?
• It is built in software that determines what
your computer can do without accessing
programs.
• It is first software run by a PC when it is
powered on.
• It is typically placed in ROM chip and often
known as a ROM-BIOS.
3. Initialization…
• The BIOS is special software that interfaces the major hardware
components of your computer with the operating system
• When you turn on your computer, the BIOS does several things. This is its
usual 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
The first thing the BIOS does is check the information stored in a tiny (64
bytes) amount of RAM located on a complementary metal oxide
semiconductor (CMOS) chip.
4. P.O.S.T.
• Power On Self Test
• Post tests and identifies system devices such as CPU, RAM,
interrupt, keyboards, DMA controllers, hard disk.
• The principal duties of the main BIOS during POST are as follows:
verify CPU registers
verify the integrity of the BIOS code itself
verify some basic components like DMA, timer, interrupt controller
find, size, and verify system main memory
initialize BIOS
identify, organize, and select which devices are available for booting
5. BIOS boot process
• If system has just been powered up (cold boot)the full
POST will run.
• But if reset button was pressed (warm boot)specific flag
value is detected in memory and BIOS does not run POST.
• This saves the time otherwise used to test all memory.
• The BIOS begins its POST when the CPU is reset.
• A little-known feature of the original IBM BIOS versions is
that before beginning the normal boot process they
would attempt to load a program through the keyboard
port.
6. User Interface…
• The BIOS in the IBM PC and XT had no built-in user-
interface.
• A modern BIOS has a menu-based user interface(UI)
accessed by pressing a certain key on the keyboard
when the PC starts. In the BIOS UI, a user can:
– configure hardware
– set the system clock
– enable or disable system components
– select which devices are potential boot devices
– set various password prompts, such as a password for
securing access to the BIOS user interface functions itself
and preventing malicious users
7. Virus Detected…
• There are four known BIOS attack viruses.
• The first BIOS virus was CIH, and able to erase flash ROM BIOS content.
• The second BIOS virus was a technique presented by John Heisman.
• He shown how to elevate privileges and read physical memory, using
malicious procedures that replaced normal functions stored in flash
memory.
• The third BIOS virus was a technique called "Persistent BIOS infection.
• Mebromi is a Trojan which targets computers with Award-
BIOS, Microsoft Windows, and antivirus software from two Chinese
companies.
• For boot sector virus, you can simply fix it using Fixboot
or use a utility to fix it.
8. Update BIOS
• Computer will need to its BIOS updated especially for older
machines.
• Download the upgrade and utility program needed to install it.
• Major BIOS manufactures include:-
– American Megatrends
– Phoenix Tech.
– ALi
– Winbond
• As we changes to the CMOS setup be careful when upgrading your
BIOS,otherwise you could corrupt the BIOS.
