The document discusses the booting process of a computer system. It explains that booting is required because the hardware does not know where the operating system is located or how to load it. It needs a bootstrap loader like the BIOS to locate the kernel in memory and start its execution. It describes the minimum files (command.com, io.sys, msdos.sys) needed to boot to a DOS prompt. The boot process begins with the CPU loading a predefined memory location containing a jump instruction to the bootstrap program (stored in ROM). The BIOS then runs diagnostics, initializes devices and memory, and loads the operating system. Secondary boot loaders like GRUB can load if the active partition is invalid

1. BOOTING OF A
COMPUTER SYSTEM
PC MAINTENANCE ASSIGNMENT

2. Why is Booting Required ?
Hardware doesn’t know where the operating system resides
and how to load it.
Need a special program to do this job – Bootstrap loader.
E.g. BIOS – Boot Input Output System.
Bootstrap loader locates the kernel, loads it into main memory
and starts its execution.

3. What files are needed to boot a PC computer?
The computer needs the minimum of the below three files to boot
to a DOS prompt.
command.com
io.sys
msdos.sys
NOTE:- The above files are the very minimum files. If an
external command such as ”Fdisk” needs to be performed

4. How Boot process occurs ?
Reset event on CPU (power up, reboot) causes instruction
register to be loaded with a predefined memory location. It
contains a jump instruction that transfers execution to the
location of Bootstrap program.
This program is form of ROM, since RAM is in unknown state at
system startup. ROM is convenient as it needs no initialization
and can’t be affected by virus.

5. BIOS Interaction

6. Tasks performed at boot up
Run diagnostics to determine the state of machine. If
diagnostics pass, booting continues.
Runs a Power-on-self-test (POST) to check the devices that the
computer will rely on, are functioning.
BIOS goes through a preconfigured list of devices until it finds
one that is bootable. If it finds no such device, an error is given
and the boot process stops.
Initializes CPU registers, device controllers and contents of the
main memory. After this, it loads the OS.

7. BIOS Setup

8. Boot Procedure

9. Secondary Boot Loaders
If there is no active partition or the active partition's boot sector
is invalid, the the master boot record (MBR) may load a
secondary boot loader and pass control to it and this secondary
boot loader will select a partition (often via user input) and load
its boot sector.
Examples of secondary boot loaders
GRUB – GRand Unified Bootloader
LILO – LInux LOader
NTLDR – NT Loader

10. GRUB Loader

11. Dual booting
Dual booting is the act of installing multiple operating systems
on a computer, and being able to choose which one to boot
when switching on the computer. The program, which makes
dual booting possible is called a boot loader.
I.E Windows 8 and Ubuntu

12. Peace & Love