Disk Drive

A disk drive is a device that allows a computer to read from and write data to a disk. The most common type of disk drive is a hard disk drive (HDD), and the terms are typically used interchangeably. Other types include optical drives, storage devices, and floppy drives. A disk drive is commonly found in PCs, servers, laptops, and storage arrays.

Disk drives can either be housed internally within a computer or housed in a separate box that is external to the computer. They work by rotating very rapidly around a head or heads that reads and writes data. Hard disk drives and removable disk drives use a magnetic head, while an optical drive uses a laser. A disk drive differs from a solid state drive (SSD), which has no moving parts and offers greater performance but also costs more and generally offers less capacity.

Parts of a disk drive

A disk drive is made up of many moving parts:

  • Platter: The platter is the actual disk inside the drive that stores the magnetized data. Traditionally, platters are made of a light aluminum alloy and coated with a magnetizable material. Newer technologies use glass and/or ceramic platters because they are thinner and more heat resistant.
  • Spindle/Motor: The platters are attached at the center to a rod or pin called a spindle that is directly attached to the shaft of the motor that controls the speed of rotation.
  • Read/Write Heads: Read/write heads read and write data to the platters. When one head is over a track, all other heads are at the same location over their respective surfaces. The read/write heads convert the electronic 0s and 1s in the magnetic fields on the disks.
  • Head-Actuator Assembly: All heads are attached to a single head actuator, or actuator arm, that moves the heads around the platters.
  • Logic Board: The platters, spindle, spindle motor, head actuator and the read/write heads are all contained in a chamber called the head disk assembly (HDA). Outside of the HDA is the logic board that controls the movements of the internal parts and controls the movement of data into and out of the drive.

Hard disk drive vs. solid state drive

Solid state drives (SSDs) have led to a decline in hard disk use and popularity. An SSD is a high-performance, plug-and-play storage device that requires no moving parts. It is faster, more durable, and uses less power than a hard disk. A major drawback of the SSD is it’s more expensive in terms of dollar per gigabyte.

An SSD fits into the same external and internal drive bay of a hard disk. While hard disks still exist in cheaper and older systems, SSDs are now used in most mainstream systems, such as the MacBook Pro. They are much faster and will boot in less than a minute. A hard disk takes time to speed up, and will almost always boot slower, launch slower, and transfer files slower. Hard disks provide much more space for the price, so it’s better for those needing high capacity.


Vangie Beal
Vangie Beal is a freelance business and technology writer covering Internet technologies and online business since the late '90s.

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