"HDD" is an abbreviation for "hard disk drive" when it is used in reference to computers. A hard disk drive is mechanical, magnetic device that is used as a primary internal storage device in computers. As of 2014, this component has been part of most computers for over 25 years.
An HDD stores data using a random-access method, allowing data blocks to be stored at any order. As of 2014, a typical HDD design includes one or more rotating disks that is fitted with a magnetic head and placed over an actuator arm that writes and reads data. The first HDD was developed and introduced by IBM in 1956.