The Master Boot Record (MBR) resides in the first 512 bytes of the hard disk. This 512 bytes contains two things:
440 bytes for the boot loader (Grub, or Windows boot loader, etc.)
The remaining space is used for the partition table, i.e.: there can only be 4 primary partition in an MBR partitioning scheme. This remaining area also has the partition location information.
This can be done by two methods:
CHS method: In this method a partition is located through cylinder, head, sector. This is described by a 24 bit number, and in this case it can only mention disk to a maximum of 8GB.
LBA method: LBA stands for Logical Block Addressing, where each and every sector is numbered serially resulting in easy addressing of spaces upto 2TB.