When the computerís boot system searches for the hard drive, the first thing
it will inspect is whether the MBR (Master Boot Record) of the first hard drive
(master of the first IDE channel or first disk of the SCSI channel) contains
any indication of the system to be loaded. The MBR is the first track of the
hard disk, where the information regarding configured partitions is stored,
and optionally, the program responsible for initiating the operating system.
If this program is not found here, the boot sector of the diskís active partition
will be inspected. Whenever we wish to install a program in the computerís
boot system we must place it in one of these zones. In the following figure
we can see this entire process when the boot sequence is first the disk drive
and then the disk:
Whenever we install a boot system, we need to remember that the order in
which this sequence is carried out is important: if we install one on the MBR
and another on the active partition, the MBRís will be executed because this
is the area that the BIOS or EFI inspects first. If we do not have an active
partition, we need to place the boot program in the MBR. At all events, the
most advisable is to always install the program on the MBR because it is the
first thing to be inspected. Although we may have other operating systems
installed on other disks, we should install Grub in one of these zones.
In the program configuration we will tell it where the operating system that
we wish to load is located.