• BIOS stands for "Basic Input/Output System", and its purpose is to provide communication between the microprocessor (CPU) and the operating system files residing on the hard drive. It is actually the first program that runs when you first turn your PC on. Without it, your operating system would never load.

BIOS's are the lowest level of software in a computer providing a set of small programs or software routines that allow the hardware of a computer to interact with the operating system by a set of standard calls.

PROCESS OF BOOTING• Power is applied to the computer.

When power is applied to the system and all output voltages from the power supply are good, the power supply will generate a power good signal which is received by the motherboard timer. When the timer receives this signal, it stops forcing a reset signal to the CPU and the CPU begins processing instructions.

• Actual boot

• The very first instruction performed by a CPU is to read the contents of a specific memory address that is pre-programmed into the CPU.

• The code that the processor reads is actually a jump command (JMP) telling the processor where to go in memory to read the BIOS ROM. This process is traditionally referred to as the bootstrap.

PROCESS OF BOOTING

• POST

POST stands for Power On Self Test. It's a series of individual functions or routines that perform various initialization and tests of the computer’s hardware. BIOS starts with a series of tests of the motherboard hardware. The CPU, math coprocessor, timer IC's, DMA controllers, and IRQ controllers.

PROCESS OF BOOTING

• Looking for the Operating System

Once POST is complete and no errors found, the BIOS will begin searching for an operating system. Typically, the BIOS will look for a DOS Volume Boot Sector on the floppy drive. If no operating system is found, it will search the next location, the hard drive C.

PROCESS OF BOOTING