Primary and Secondary Partitions
A hard disk can be partitioned into up to four partitions. This is due to the table where the position and size of the individual partitions is stored (partition table). This partition table was specified in the beginning of the 80s and is basically still the current status of technology. Since this partition table represents the first division, it is called the "primary partition table."
Several operating system developers combined their efforts to introduce a new standard. This new standard was to enable the subdivision of each of the four basic partitions into several parts (partitions). To achieve this, a different type of partition table storage is utilized, which has the potential of allowing an unlimited number of entries.
This divided partition is actually no partition in the true sense of the word because it cannot - and is not supposed to - contain any file system itself. It only serves to extend the option of partitioning the hard disk. This type of partition is thus usually called an "extended partition."
The partition table within this partition is then referred to as the "extended partition table" or more exactly the "secondary partition table."
These partitions (within this extended partition) are called "secondary partitions" or "logical drives." (The latter term, however, is not quite accurate since in technical terms, primary partitions are also nothing more than a logical division of the physical hard disk and are thus logical drives as well.)
The technical differentiation between primary and secondary partitions is almost exclusively based on the entry within the respective partition table.
Not nearly all operating systems, however, have put secondary and primary partitions in the same category. For example, when booting from secondary partitions created with Microsoft operating systems certain restrictions apply.