BIOS basic input output system
- 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.