We usually say the zoning concepts, no more than three types: primary partitions, extended partitions and logical partitions. The primary partition is a relatively simple partition, usually located on the top of a hard disk area, constitutes a logical C disk. In the main partition, it’s not allowed to re-establish other logical disks.
 The concept of extended partitions is more complex and also the main reason contributed to the confusion of the partition and logical disks. As the hard disk partition table reserved only for 64 bytes of storage space, while the parameters of each partition occupies 16 bytes, so the main boot sector can be stored in a total of four partitions of data.
The operating system only allows four partitions of the data is stored, if the disk is a logical partition, the system only allows a maximum of four logical disks. For specific applications, four logical disks often do not meet the actual demand. In order to build more logic disk for the operating system to use, the system introduces the concept of extended partitions.
