Bootstrapping

Booting is the process of loading operating system into main memory. For a computer to start running, it needs to have an initial program to load and execute the boot program, which in turn loads the operating system. This primitive loader program that can load and execute the boot program is called Bootstrap program. Bootstrap program is typically stored in ROM. On-start up; the computer automatically reads the bootstrap program. This primitive loader is then executed and loads the boot program in predetermined memory locations. The boot program is generally stored on disk with predetermined address, called boot sector. The boot program then loads the operating system into memory. This arrangement is known as bootstrapping.

Consider an example, the boot process in Windows 200 operating system. The windows 2000 operating system store its boot code in the first sector of the hard disk (known as Master Boot Record or MBR).

Windows systems allow us to logically divide the physical hard disk into one or more partitions, one partition identifies as the boot partition usually known as primary partition. The boot partition is normally used to store operating systems code and other device drivers. While switch on the system, booting begins by running bootstrap program that is resident in the system’s ROM memory. The bootstrap program then instructs the systems to load the boot code form the MBR. In addition to the boot code the MBR contains a table listing the details about the partitions for the hard disk and it also indicate which partition is used as the boot partition by setting certain flags. Once the system determines the boot partition then it starts to read the first sector from that particular partition and continue with the boot process. 

In the case of Windows XP, NTLDR is used to determine which device contains the operating system to load. Then the Hardware Abstraction Library (HAL) is load by NTLDR. NTLDR also loads the kernel and the system hive for the device.

More about Windows operating system and its working will discuss later.

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