Hard Disk Drive (HDD), hard disk or hard drive is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital data using one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data even when powered off. HDD performance is specified by the time required to move the heads to a track or cylinder adding the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and the speed at which the data is transmitted. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA) and SATA (Serial ATA). SATA is the latest.