A hard drive that is outside of the computer case in its own enclosure. Most external hard drives support the IDE interface and are slightly bigger than a hard drive itself. When purchasing an external hard drive you can buy a full external hard drive system that consists of both the hard drive and the enclosure, or you can purchase just the enclosure to hold your own hard drive.
External hard drives may contain a fan for cooling and are popular because they are portable devices and can be stored securely under lock and key since they are not inside the computer case. An external hard drive is connected to the computer system with a single high-speed interface cable, usually with plug-and-play interfaces such as USB or FireWire.
Hard drive enclosures, also called hard drive cages are made to support up to a certain physical size of hard disk, so you need to check the manufacturer’s specification when buying just the enclosure.
See hard disk drive.