Brief History

• The original specification for hard disks allows up to four partitions per physical device. Any partition defined would have been a "primary" partition, suitable for booting. Microsoft MS-DOS version 3.3 introduced the "extended" partition, opening the way for one physical drive to be sub-divided into any number of smaller "logical" drives.
  
  

About Primary Partitions

• All primary partitions are found within the Master Boot Record (MBR) in the first part of the hard disk, or "sector zero." The BIOS in a PC looks to the MBR when booting the operating system, usually from the first primary partition. Although alternate configurations may be possible, installing the operating system to a primary partition is always strongly recommended.
  
  

About Extended Partitions

• Extended partitions are misunderstood, because they do not themselves contain a formatted drive. An extended partition is like a virtual container; allowing one or more "logical volumes" within it. An extended partition is typically unsuitable for booting an operating system.
  
  

Drive Letter Assignment (PCs using MS Windows®)

• Starting with MS-DOS®, a Microsoft operating system would assign letters (starting with "C:") for each drive or volume that it can read and understand. By default, the system assigns letters for primary drives first, then logical drives. If two hard disks are installed, where disk1 has one primary partition and one extended partition with two logical volumes, but disk2 has just one primary partition, the system assigns letters C:, E: and F: to volumes on disk1 and D: to the volume on disk2.
  
  

Mounted Directories (Linux-based systems)

• In Linux, only the root volume (path: /) needs to be a primary partition. All other mounted directories may be part of an extended partition, including /boot, /var, /tmp, /home and /usr. Planning out your hard disk to use multiple volumes for these directories can provide significant performance and security benefits.
  
  

Planning Your Hard Disk

• Each computer is unique and therefore the best partitioning scheme is unique to each computer. One essential fact about hard disks--they start at the outermost track (where the disk surface moves faster) and count inward to the innermost track (where it moves slower). Keeping active data---such as programs and the operating system itself---near the start of the hard disk will always give better performance.