A Description of the Boot Process

The computer's power is first turned on, the CPU initializes itself, which is processed by a series of clock ticks generated by the system clock. CPU's initializes the system's ROM BIOS for the first instruction in the startup program. The ROM BIOS stores the first instruction, which is the instruction to run the power-on self test (POST), in a predetermined memory address. POST begins by checking the BIOS chip and then tests CMOS RAM. If the POST does not detect a battery failure, it then continues to initialize the CPU, checking the inventoried hardware devices (such as the video card), secondary storage devices, such as hard drives and floppy drives, ports and other hardware devices, such as the key board and mouse, to ensure they are functioning properly. Once the POST has determined that all components are functioning properly and the CPU has successfully initialized the BIOS looks for an OS to load.

Once the OS initializes, the BIOS copies its files into memory and the OS basically takes over control of the boot process. Now in control, the OS performs another inventory of the system's memory and memory availability (BIOS already checked one) and loads the device drivers that it needs to control the devices, such as a printer, scanner, optical drive, mouse and keyboard. This is the last stage in the boot process, after that the user can access the system’s applications to perform tasks.