In order for the BIOS to load an OS it looks
for instructions on the first sector of a hard drive.
On the first sector of the hard drive resides
the master boot record (MBR), and is where a boot loader is initialized.
Depending on the boot loader, additional files
may be stored and read from a partition on the hard drive.
After this step the boot loader begins to
start the operating system, and is not used again until the next boot.
