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BIOS stands for Basic Input/Output System. It contains basic instructions to interact with various hardware modules such as Motherboard controllers or that of interface cards. BIOS is the software that is run by a computer when first powered on. A computer motherboard inevitably contains a BIOS chip in the form of an onboard PROM, EPROM or flash memory. When the computer is powered on, it performs diagnostic tests on the computer hardware devices such as hard drive, FDD, and memory. It searches for other BIOS's on the plug-in boards, and takes care of them. It then loads the operating system and passes control to OS. The BIOS accepts requests from the drivers as well as the applications as shown in the figure below. |
BIOS is also known as PC firmware because it is an integral part of the motherboard.
Firmware on adapter cards: A computer can contain several BIOS firmware chips. The motherboard BIOS is normally used to access basic hardware components such as the keyboard, floppy drives, and hard disk controllers. Adapter cards such as SCSI, RAID, and video boards may include their own BIOS software.
Firmware generally available in different forms:
1. EPROM (Erasable Programmable ROM), for updating a BIOS firm using EPROM,
you may need to get a new chip from the manufacturer.
2. EEPROM (Electrically Erasable Programmable ROM), you can update a BIOS
firmware using EEPROM using "boot to floppy", and running the Firmware
update program.
3. Flash ROM - faster at rewriting the chip
A typical BIOS chip used on motherboards is shown in the figure below. Though it is a square-type PLCC package, BIOS chips come in different forms. Figure 2 shows the BIOS after insertion into the socket.:
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| BIOS chip | BIOS chip after insertion into a socket. |
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