External removable hard disk drives offer independence from system integration, establishing communication via connectivity options, such as USB.Plug and play drive functionality offers system compatibility, and features large volume data storage options, but maintains a portable design.

These drives with an ability to function and be removed simplistically, have had further applications due their flexibility. These include:Disk cloning,Data storage,Data recovery,Backup of files and information,Storing and running virtual machines,Scratch disk for video editing applications and video recording,Booting operating systems (e.g. Linux, Windows, Windows To Go – a.k.a. Live USB).External hard disk drives are available in two main sizes (physical size), 2.5" and 3.5".Features such as biometric security or multiple interfaces are available at a higher cost.

More than 200 companies have manufactured hard disk drives over time. As of December 2010, most hard drives are made by: Western Digital (31.2%),Seagate (29.2%),Hitachi GST (18.1%) (being sold to Western Digital),Toshiba (10.8%),Samsung (10.7%) (being sold to Seagate)