By putting its code in the boot sector, a virus can guarantee it's executed.
This is analogous to the boot sector of a hard disk.
The command can be applied to hard drives and floppy disks to repair or create a boot sector.
The real boot sector is moved to another sector and marked as bad.
The boot sector can sometimes be recreated more easily than saving it.
Ontario.2048 does contain a boot sector within it with a boot virus.
And so it is this altered boot sector which gets control as the system boots before Windows does.
It looks just like a hard drive with a boot sector.
Surely Win8 doesn't keep the private portion of the "encrypt the boot sector" in memory.
I ask because in any Windows installation the boot sector of the hard drive is always a constant.