Booting Process Of Your Computer

The Booting process involved a well organized procedure to perform all system checks and loads all necessary files to bring the computer to an operable state. This process is also known as bootstrap. Generally there are two types of booting. First one is Cold boot which is used when you turn the computer on from an off position and the other is Warm boot is used when you reset a computer that is already on. Most of the people are not aware about the processes involved in the Booting. In this article I will let you know all the processes in detail manner. Following processes are involved in booting:

• First of all BIOS (Basic Input Output System) comes into picture which is the first code executed by computer when power supply is switched on. When power is turned on, POST (Power-On Self-Test) is the diagnostic testing sequence which is performed by computer to determine if the peripheral devices like computer keyboard, disk drives and other hardware are working correctly. If the POST is a failure the system halts with a beep sound.
•  Then BIOS checks the boot priority. We can set the boot priority as CD drive, hard disk or flash memory.
• The next duty of BIOS is to read the MBR (Master Boot Record).The first sector on a hard disk. MBR contains the partition loader and boot loader.

       Function of Partition table:

• The partition loader code which accesses the partition table to identify the primary partition, extended partitions and active partition which is needed to determine the file system and locate the operating system loader file - NTLDR.
• NTLDR will call upon the boot.ini file which is located at the root directory to determine the location and entries of the operating system boot partition. NTLDR will pass all information from the Windows registry and Boot.ini file into Ntoskrnl.exe.

       Function of Bootloader:

Then Boot loader performs tasks of loading operating system in the memory. Generally two terms are used the Cold boot is used when you turn the computer on from an off position and the Warm boot is used when you reset a computer that is already on. The two stages are involved in the boot loader, stage 1 boot loader and stage 2 bootloader. MBR contains the stage 1 boot loader and stage 1 boot loader is a link to the stage 2 boot loader. The stage 2 boot loader resides in the boot partition and it loads the kernel to the computer memory.

Boot files and functions:

There are three boot files in a Windows operating system and they are found in the active partition of hard disk and its normally C drive:

1.NTLDR: - NTLDR stands for NT Loader and it’s the second stage bootloader.

2.Boot.ini: - Boot.ini contains the configuration files of NTLDR. When the operating system is loaded we cannot pass any arguments to kernel, so those arguments are passed through boot.ini.

3.NTDETECT.COM: - This file detects hardware's and passes information to NTLDR to create a hardware key for hardware detection. A new hardware key is generated after each reboot of the operating system and that's why system asks to reboot after installation of a new hardware.

Kernel and its functions:

After executing the functions of boot files the control is passed to Kernel. Ntoskrnal.exe is    the kernel file in a Windows machine. Kernel acts as a layer between software and hardware. The library file hal.dll helps Kernel to interact with hardware's. HAL stands for Hardware Abstraction Layer and this hal.dll file is machine specific. Now the drivers for hardware's are loaded from the file and the Kernel is loaded to primary memory.

Services and log in procedure:

When kernel is loaded in the primary memory services for each process is started and the registry entry occurs. Winlogon.exe starts the log in procedures of windows machine. It first calls the library file msgina.dll which provides the log in window. Now msginal.dll passes the control to LSA (Local Security Authority), it verifies the username and password from the SAM file. SAM file contains information about all users of that install Window operating system.