POSTs (Power-On-Self-Tests): It the first instruction in ROM BIOS. When system is powered on, hardware self-tests are performed such as battery failure, if battery is not failed it continues to initialize CPU having Adapters.

ADAPTERS: After running POST, the system initializes each adapter. If the adapter has its own built-in BIOS, the adapter's BIOS is called to perform its own initialization.For IDE adapters (Integrated Development Environment-is packed as an application program typically consisting of a code, a compiler, a debugger and a graphical user interface [GUI] builder, most computers have either two or four IDE adapters), each connected drive (there may be up to two drives for each IDE adapter, allowing for a total maximum of eight IDE type drives) is queried for its specifications and access method.Some adapters, such as Adaptec's SCSI adapter’s (Small Computer System Interface Controller), display messages and allow the user to interact.

>MBR (Master Boot Record): After all the adapters that have a BIOS have been initialized, the system boot loader reads in the sector located at the very beginning of the first bootable disk drive and passes commands to this code. This sector is called the boot sector, or the MBR (Master Boot Record), and it is written by the operating system when the operating system is installed.

The code in the MBR then loads and passes control to theNTLDR(New Technology Loader) file (windows xp boot loader, now in windows 7&8 it is replaced by BOOTMGR file).

> NTLDR (or BOOTMGR): NTLDR then loads a special copy of the necessary file systemI/O files and reads in the file boot.ini (windows xp boot configuration file, now in windows 7&8 it is replaced with the Boot Configuration Database (BCD) lives in boot folder of the System volume).

>boot.ini(in win xp) (or)BCD (Boot Configuration Database)(in win 7&8): Encrypted BCD log file is shown below haasini. The file boot.ini has information about each operating system that can be

loaded.

NTLDR then processes boot.ini, displaying boot information that allows the user to select which operating system will be loaded.

After selecting the O.S, NTLDR loads the file ntdetect.com.

>NTDETECT.COM: This program then collects information about the currently installed hardware and saves this information for the registry. Most of this information is stored in theHKEY_LOCAL_MACHINE hive.

Once NTDETECT has detected the hardware, control is passedback to NTLDR, and the boot process continues. At this point, the registry has been substantially updated with the current hardware configuration, which is stored in HKEY_LOCAL_MACHINE\Hardware.

Following the detection of NTDETECT, NTLDR loads Winload.exe

>Winload.exe: It loads and initializes the Windows NT kernel (ntoskrnl), loads the services, and then starts Windows.

When the kernel is loaded, the HAL is also loaded. (The HALHardware Abstraction Layer—is used to manage hardware services.) Next, the registry system sub-key HKEY_LOCAL_MACHINE\_System is loaded into memory.

Windows scans the registry for all drivers with a start value ofzero. This includes those drivers that should be loaded and initialized at boot time.

From this point, Windows starts various components and systems. Each component and system reads the registry and performs various tasks and functions. In the final stage, the program that manages the user logon, WinLogon, starts..