1.1.2 Extended Partitions

The primary partition table of a hard drive resides in the first sector of the hard drive, which is known as the Master Boot Record, or MBR. One entry in the primary partition table may be an extended partition. An extended partition is a partition that can hold a chain of other partitions within it. The first sector of an extended partition contains a partition table which is of the same form as the primary partition table.

The convention used by MS DOS is to only use the first two entries in partition tables within the extended partition. The first entry will define a usable partition (if any). If another partition after the current one exists in the extended partition, then the second entry in the partition table will point to the next partition table. Otherwise, it will be blank, indicating that it is the last partition in the chain.

MS DOS stops parsing a partition table when it has either read four entries, or encountered a blank entry. A partition can be hidden by being placed after a blank entry.