What part of a PC is the hard drive?

The hard drive is one of the most important components of a personal computer (PC). It provides long-term storage for all of the software, applications, files, photos, videos, and other data on the computer. Understanding where the hard drive is located and how it functions is key to properly using and maintaining a PC.

Quick Answer

The hard drive is a storage device located inside the computer case that reads and writes data on internal disk platters. It connects to the motherboard via cable interfaces like SATA, ATA, or SCSI. The hard drive is a non-volatile storage device, meaning it retains data even when the power is turned off.

What is a Hard Drive?

A hard disk drive, commonly referred to as a hard drive or HDD, is a data storage device used in computers to store and retrieve digital data using rapidly rotating disks coated with magnetic material. The platters are paired with magnetic heads arranged on a moving actuator arm, which reads and writes data to the platter surfaces.

Because hard drives have high storage capacity and are non-volatile (they retain data even when powered off), they are ideal for long-term secondary storage. When a computer is powered on, files and programs are loaded from the hard drive into the computer’s working memory or RAM to be accessed by the CPU. The hard drive allows permanent data storage on your PC.

Hard Drive History

The first commercial hard drive was invented in 1956 by IBM and consisted of 50 2-foot wide disks stacked vertically, weighing over a ton, and storing 5 MB of data. Capacity steadily improved over time with technological advances. The first 1 GB hard drive was not developed until the 1980s.

Today, desktop hard drives can store upwards of 10 TB, while high-capacity enterprise hard drives for servers and data centers can store up to 20 TB or more. Hard drive capacities continue to grow rapidly as technology improves.

How a Hard Drive Works

A modern hard drive contains one or more rigid platters inside of an air-sealed enclosure. Platters are made of a non-magnetic material, usually aluminum alloy, glass, or ceramic. These platters are coated with a thin layer of magnetic material that stores the binary data – either a 1 or a 0.

The platters spin rapidly around a central spindle and information is accessed by an actuator arm mechanism containing read/write heads for each platter surface. The heads float nanometers above the drive surface on an air bearing created by the disk’s aerodynamics.

Data is stored in concentric tracks that divide each platter surface into billions of bytesized storage locations. As data needs to be written or read, the actuator arm moves the heads to the proper track location and the heads detect or change the magnetic orientations of the platter surface.

The disk controller manages the flow of data to and from the drive through an interface standard like SATA, ATA, SCSI, SAS, or Fibre Channel. The controller directs the mechanical operation and transforms logical data requests into physical storage and retrieval actions.

Hard Drive Components

While hard drive designs vary, they all contain the same core components that work together to manage, write, and access data:

  • Platters: The layered disks that data is stored upon. Made of non-magnetic material like aluminum, glass, or ceramic and coated with a thin magnetic layer.
  • Spindle: A shaft in the center of the drive around which the platters rotate.
  • Read/Write Heads: Located on the actuator arm, these heads are responsible for writing data to the platters or reading data from them.
  • Actuator Arm and Actuator: Moves the heads to the proper track location to access data.
  • Motor: Spins the spindle and platters at high speeds, usually between 5,400 and 15,000 RPM.
  • Head Actuator: Controls the positioning of the actuator arm.
  • Firmware: Low-level software that handles drive operations like motor spin control, data management, error detection and recovery.
  • Casing: Sealed metal or metal alloy enclosure that protects the internal components.
  • Controller: Circuit board with the electronics that manage and coordinate all of the components.
  • Interface: Allows communication between the drive and computer, usually SATA, ATA, SCSI, SAS or Fibre Channel.
  • Cache: Provides faster access to frequently accessed data.

Hard Drive Interfaces

One of the most important components is the interface, which enables data to be transferred between the hard drive and computer. Here are some common hard drive interface types and speeds:


Serial ATA or SATA has surpassed Parallel ATA (PATA) as the most common hard drive interface type. SATA separates control signals from data signals, enabling faster data transfer speeds. The current SATA III standard provides 6 Gbps speeds.


Serial Attached SCSI or SAS is frequently used in servers and enterprise hard drives. It provides fast 12 Gbps transfer speeds using the SCSI command set and point-to-point serial connections.


The SCSI or Small Computer System Interface was very popular for connecting hard drives before SATA, SAS, and Fibre Channel became widespread. It offers transfer speeds up to 320 MBps through a parallel bus interface.

Fibre Channel

Fibre channel is a high-speed interface used for storage networks and devices where very fast data transfer is required. It provides up to 16 Gbps throughput.


Integrated Drive Electronics or IDE was renamed to ATA and utilizes a parallel data interface to connect the hard drive to the PC’s motherboard. The last version called Ultra ATA or Ultra DMA supports up to 133 MBps transfers.

Hard Drive Form Factors

Hard drives come in different physical configurations known as form factors. The form factor impacts the interface, size, mounting, and usage of the hard drive. Common form factors include:


The most popular form factor for desktop PCs, 3.5-inch hard drives fit into drive bays and are mounted via built-in screw holes or rails. They require both 5V and 12V power from the PC power supply unit.


Smaller 2.5-inch hard drives are designed for mobile devices and laptops. Many are enclosed in a metal case and use the SATA interface. No mounting is required, only a SATA and power connection.


Very small 1.8-inch hard drives with 1-2 platters were designed for mobile devices like digital audio players and some laptops. ZIF connector types were common.


Extremely tiny 1-inch hard drives existed for portable consumer electronics like MP3 players. The Microdrive by IBM utilized a single platter in a CompactFlash form factor.

Where is the Hard Drive Located?

Knowing where the hard drive is placed inside a desktop PC case makes it easier to identify, add, or replace a drive if needed.

3.5-inch Desktop Hard Drives

3.5-inch hard drives designed for desktop computers are usually mounted into dedicated drive bays on the front panel of the PC case. The bays may use rails, trays, or screw holes to secure the hard drive in place.

Cables connect the hard drive to the motherboard, including the SATA or PATA data cable and a power cable from the power supply unit. This provides the drive with communication and power from the PC to operate.

2.5-inch Laptop Hard Drives

For laptops, 2.5-inch hard drives are mounted internally in the laptop chassis. In many cases, an access panel on the bottom of the laptop allows the hard drive to be removed and replaced. Some laptops feature easily accessible hard drive bay compartments.

The laptop SATA cable plugs into the hard drive interface to connect it to the motherboard. Power is provided through the laptop power system so no extra cabling is required.


In summary, the hard drive is one of the most vital internal components in a computer system, providing permanent and large capacity storage capabilities. All PCs contain at least one hard drive, which reads and writes data from fast spinning disk platters using magnetic heads.

Hard drives come in 3.5-inch and 2.5-inch form factors, with the 3.5-inch drives mounted in drive bays on desktop PC cases. The drive connects to the motherboard through SATA, SAS, or other interface cables to enable data communication. Understanding the role and location of the hard drive makes it easier to use and maintain your computer.

The hard drive’s function as long-term secondary storage that retains files even when powered off makes it an essential component of any PC. As one of the earliest computer storage devices, hard drive technology continues advancing rapidly to provide greater speed and enormous capacity compared to early hard drives.

With terabyte and even multi-terabyte drives now commonplace, hard drives store more data than ever before. New innovations like shingled magnetic recording and heat-assisted magnetic recording pave the way for harder drive improvements in the future. Even with the emergence of SSDs for some roles, the hard drive remains an integral part of computing.

Knowing where the hard drive resides within a desktop PC and how it works sheds light on an important internal component. This helps users better utilize and maintain the vital storage space within their computer. As programs, operating systems, photos, and files consume more space than ever, the hard drive continues offering abundant long-term storage capacity to PCs for years to come.