During POST, the BIOS also locates the system boot device—such as the floppy
disk, CD-ROM, or hard drive—that contains the OS. Once the POST process
completes successfully, the BIOS then passes control of the boot process over to
the PC’s OS. The exact loading process differs from one OS to the next, but in
general, one or more vital system files such as NTLDR (pronounced “NT
loader”) load into memory and start the ball rolling. Things move fast from
there, as the OS load its core files, drivers, and services into RAM.The next thing
you know, you’re looking at your desktop and hearing the soothing strains of
the Windows logon sound file.