1. The partition table has room for only four partitions. For more partitions, one of these four partitions can be divided into many smaller partitions, called logical partitions. The original four are then called primary partitions. If a primary partition is subdivided in this way, it is known as an extended primary or extended partition. Typically, the first primary partition will be small ( /dev/hda1, say). The second primary partition will fill the rest of the disk as an extended partition ( /dev/hda2, say). In this case, the entries in the partition table of /dev/hda3 and /dev/hda4 will be blank. The extended partition can be subdivided repeatedly to give /dev/hda5, /dev/hda6, and so on. From Rute-Users-Guide