When the computer is switched on, a
copy of boot program is brought from ROM into the main memory. This process is
called booting. The CPU first runs a jump instruction that transfers to BIOS
(Basic Input Output System) and it starts executing. The BIOS conducts a series
of self-diagnostic tests called POST (Power On Self-Test). These tests include
memory tests, configuring and starting video circuitry, configuring the
system’s hardware and checking other devices that help to function the computer
properly. Thereafter the BIOS locates a bootable drive to load the boot sector.
The execution is then transferred to the Boot Strap Loader program on the boot
sector which loads and executes the operating system. If the boot sector is on
the hard drive then it will have a Master Boot record (MBR) which checks the
partition table for active partition. If found, the MBR loads that partition’s
boot sector and executes it. Booting Process is of two types – Warm and Cold.
Cold Booting: When the system
starts from initial state i.e. it is switched on, we call it cold booting or
Hard Booting. When the user presses the Power button, the instructions are read
from the ROM to initiate the booting process.
Warm Booting: When the system
restarts or when Reset button is pressed, we call it Warm Booting or Soft
Booting. The system does not start from initial state and so all diagnostic
tests need not be carried out in this case. There are chances of data loss and system
damage as the data might not have been stored properly.
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