External hard drive

An external hard drive is a hard disk which is meant to be placed outside of the computer case. This allows expandability even if a computer s drive bays are full, and also provides an easily removable form of mass storage with very large capacity.

External hard drives can either be made by a manufacturer or created by putting a standard hard disk inside an external drive enclosure. The outer casing provides additional protection to the internal components and also supplies the needed connections and power. Some manufacturered external hard drives feature the ability to backup a computer s hard disk from the external drive itself.

A variety of connections are used to connect external hard drives. SCSI and SATA connections are used when the corresponding type of hard drive is inside, with the case containing a simple pass through. USB and FireWire connections require circuitry to convert the hard disk s connection, which is usually Advanced Technology Attachment, to USB, firewire, or both. IDE hard disks use this solution most frequently due to the cable length limitations of IDE. 2.5 drives have low enough power requirements to be powered off the USB or firewire bus, while 3.5 drives will require a power adapter.