Booting the Operating System

After the computer has passed the POST, the computer will start the boot process. This process is what loads the operating system and all of it's associated files. Because Microsoft Windows is the most commonly used operating system, this section will cover the process of loading Microsoft Windows.

The BIOS first hands control over to the bootstrap loader, which looks at the boot sector of the hard drive. If your boot sequence in CMOS setup is not setup to look at the hard drive first, it may look at the boot sector on any inserted floppy disk drive or optical disc first before doing this.

In this example, the Microsoft Windows XP NT Loader (NTLDR) is found on the boot sector and tells the computer where to find the remaining code on the hard drive. Next, Windows loads the ntdetect.com file, which displays the Windows splash screen and loads the Windows Registry. After loading the Registry, Windows begins to load dozens of low-level programs that make up the operating system into memory. Many of the initially loaded programs are what allow Windows to communicate with the essential hardware and other programs running on the computer.

After the Registry has loaded the initial basic hardware devices, it begins to load Plug-and-Play devices, PCI, and ISA devices. After loading all these devices, Windows loads full support of the hard drive, partitions, and any other disk drives and then moves to all other drivers that have been installed.

Finally, after successfully completing the above steps any additional required services are loaded and Windows starts.