What are the parts of a hard drive called?

A hard drive, also known as a hard disk drive (HDD), is a key component of computers and many other digital devices. It provides non-volatile data storage, which means it retains data even when powered off. Hard drives consist of several intricate parts that work together to store and retrieve data.

Main Components of a Hard Drive

The main components that make up a hard drive are:

  • Platters
  • Spindle
  • Read/write heads
  • Actuator arm
  • Voice-coil motor
  • Circuit board
  • Cables and connectors
  • Casing


Platters are the disks inside the hard drive that actually hold the data. Modern hard drives typically have multiple platters stacked on top of each other and attached to a spindle. The platters are made from non-magnetic material, usually aluminum alloy or glass, and are coated with a very thin layer of magnetic material.

Data is written and read magnetically to the platter surface using the read/write heads. The platters spin rapidly, allowing the heads to access data across the entire surface. More platters equal more surface area, which equates to more storage capacity.


The spindle is a rod that runs through the center of the stacked platters and connects them together. It spins the platters at very high speeds, typically 5,400 to 15,000 RPM in consumer hard drives.

The spindle is turned by a spindle motor, also called a drive motor, which is essentially an electromagnet. It receives power from the hard drive’s built-in circuitry.

Read/Write Heads

Read/write heads are the components that actually read and write data to and from the platter surfaces. There is one head for each platter surface.

The heads float nanometers above the platters on an air bearing generated by the disk’s own rotation. They use electromagnetism to detect and modify the magnetic orientation of tiny areas on the platters. This is how binary data gets written and read.

The heads are extremely delicate and susceptible to damage from even microscopic dust particles. This is why hard drives must remain free of contaminants during operation.

Actuator Arm

The actuator arm holds the read/write heads in place over the platters. It is a movable armature that enables the heads to access data across the entire radius of each platter surface.

It moves the heads rapidly and with high precision across the platters in tiny increments measured in nanometers. This radial movement is known as a “seek” and it allows the heads to access any data location on demand.

Voice-Coil Motor

The voice-coil motor (VCM) powers the movement of the actuator arm. It gets its name from functioning similarly to a speaker coil, but with reversed operation.

It consists of a permanent magnet setup that surrounds a coil of wire on the actuator arm. Alternating current running through the coil generates a shifting magnetic field that causes the coil to move rapidly back and forth. This in turn moves the arm and heads.

Hard drives calibrate and control the current through the VCM to achieve precise head positioning.

Circuit Board

The circuit board serves as the brains of the hard drive, processing all of the logic and commands that operate the drive. It contains the following key components:

  • Processor – Interprets commands and runs the drive firmware.
  • Motor controller – Controls the spindle motor speed.
  • actuator – Controls the VCM and actuator arm.
  • RAM – Provides fast temporary data caching.
  • ROM – Stores the drive’s firmware.

The circuit board also includes the interface and connectors that allow the drive to communicate with the host computer.

Cables and Connectors

Cables and connectors are how data gets transferred between the hard drive and computer. Common interfaces found in modern hard drives include:

  • SATA – Serial ATA, used in most desktop/laptop computers.
  • SAS – Serial Attached SCSI, used in servers and enterprise.
  • USB – Universal Serial Bus, often used for external hard drives.

Some common data connectors for these interfaces are SATA, SAS, and USB-A. The connectors plug into mate ports on the motherboard to establish the data link between drive and computer.


The casing (also called the enclosure) houses all the parts in a protective metal or plastic housing. It includes holes and ports to allow for airflow and cable connections.

For internal hard drives, the casing is part of the drive itself. For external drives, it’s the separate housing that protects the internal drive and connects it to the computer.

How the Parts Work Together

All the components of a hard drive work together in perfect synchrony to accurately and rapidly read and write data. Here is a simplified overview of the operation:

  1. The platters spin at extremely high, consistent speeds thanks to the spindle and spindle motor.
  2. The actuator arm positions the read/write heads over the platter surfaces.
  3. The heads magnetically detect and modify data bits on the platter surface.
  4. The voice-coil motor rapidly repositions the heads as needed.
  5. The circuit board processes instructions, moves the heads, and transfers data via the interface.
  6. Cables connect the drive to the host computer for data transmission.
  7. The casing seals the components from outside contamination.

This coordinated interaction allows hard drives to reliably store vast amounts of data and provide extremely fast data access. It all takes place automatically in responses to basic commands from the host computer.

Types of Hard Drives

While the basic components and operation of a hard drive are universal, some different common types of hard drives include:

HDD (Hard Disk Drive)

This refers to traditional magnetic hard drives as explained above. HDDs spin platters to read/write data magnetically using heads.

SSD (Solid State Drive)

SSDs use integrated flash memory chips and contain no moving parts. They are faster, quieter, and less prone to mechanical failure than HDDs.

Hybrid Drive

Hybrid drives combine an HDD with a smaller SSD to get improved speed and performance. Frequently accessed data gets cached on the faster SSD.

RAID Array

RAID (Redundant Array of Independent Disks) links multiple hard drives together into a single logical unit. This can improve performance and/or redundancy.

Drive Type Components Pros Cons
HDD Magnetic platters, read/write heads, moving parts High capacity, inexpensive Slower, mechanical failures
SSD Flash memory, no moving parts Very fast, shock resistant Lower capacities, expensive
Hybrid HDD + smaller SSD Improved speed over HDD alone Complexity, cost vs full SSD
RAID Multiple drives linked together Faster, more redundant More drives = higher cost


Hard drives are complex, precision data storage devices with many parts working together seamlessly. The main components include platters, read/write heads, spindle, actuator arm, voice-coil motor, circuit board, cables, casing, and more. Understanding how hard drives work helps explain their speed, capacity, and reliability considerations.

While internally they are intricate electromechanical devices, hard drives simply appear as a fast, vast data storage repository to computers. Their design allows robust long-term data storage and quick access that has enabled the information technology revolution.