What Is a Hard Disk Drive (HDD)?

Every computer you’re working on needs a place to store its data. That data could be user files, programs, an operating system, or any other information it uses or generates. A computer has to keep all this data internally on a storage device. A hard disk drive is one example and usually the most substantial hardware storage device. In this article, learn what a hard drive is, how it works, what it does, and so much more.

What is a hard drive?

A hard drive, also known as a hard disk drive (HDD), is a storage device used on many computer devices. It stores all of your digital data using magnetic fields. Your documents, photos, videos, music, applications, programs, and the operating system represent digital content stored on a hard drive.

A hard disk drive

Hard drives are non-volatile data storage devices, meaning they retain their data even when powered off. Generally, a computer has two types of memory: primary and secondary memory. Primary memory, such as RAM, is volatile. A drive, on the other hand, is secondary storage for keeping data permanently.

Popular devices such as desktop computers, laptops, mobile phones, and consumer electronics have hard drives installed to store data on a long-term basis. The configuration of these HDDs is done by dedicated storage specialists in data centers. 

Most hard drives are located internally in a PC and connect to the motherboard using an interface like an ATA (Advanced Technology Attachment), SATA (Serial AT Attachment) or SCSI (small computer system interface) cable.  In addition, a connection to the computer's PSU powers the hard drives. Hard disk drives come in different capacities, ranging from megabytes (MB) and gigabytes (GB) to terabytes (TB) of storage space.

Stand-alone storage devices or external hard drives are also available. These devices connect to your computer via a USB cable or other interface. It offers additional storage space for data backup, large files, or transferring data between machines.

How does a hard drive work? 

A hard disk drive can likely hold more information than your local library. The most surprising thing is how it stores so much content in such a small space. 

Your desktop’s hard drive employs magnetic storage technologies to save and retrieve digital content. Physically, it consists of spinning disk platters coated with a magnetic material. 

Data is stored by magnetizing tiny portions of this material on the surface of the platters. These magnetized regions represent the 0s and 1s of binary code. Each platter has a head that moves quickly back and forth across the platter so that the device can read or write data as needed via magnetic changes on the disk's surface. 

A motor spins the platters at high speeds, typically up to 15,000 RPM for high-end HDDs. The faster the platter rotates, the quicker your computer can access information from it.

To read data, the head detects the magnetic patterns on the platters. The specific magnetization pattern tells the head whether it's a 0 or a 1. When it comes to data writing, the head generates a magnetic field that flips the polarity of the magnetic regions on the platter to create the desired pattern of 0s and 1s.

Note that the actuator arm is what positions the read-write head in the desired location on the platters. Overall, the precise mechanics of a hard drive allow for efficient data storage.

Components of a hard disk drive 

At the heart of every hard drive is a set of essential parts that are responsible for its functioning. They are:

  • Disk platters, which are circular disks made of aluminum or glass and coated with a special magnetic material. Data is stored by magnetizing tiny portions of the material on the surface of the platters. There can be one or more platters in a hard drive stacked on a central spindle.
  • Spindles, which are motors that spin the platters at high speeds. The speed ranges from 5,400 to 7,200 RPM (rotations per minute) for conventional HDDs. The high speed allows for faster data access.
  • Read-write heads, which are tiny electromagnetic devices that float close to the surface of the platters. They can detect the magnetic patterns on the platters to read data and manipulate the magnetic fields to write data.
  • Actuator arms, which precisely position the read-write heads over the desired location on the platters. They move rapidly and accurately to access different parts of the platters.
  • Disk controllers. Disk controllers are the brain of the hard drive, controlling the movement of the read/write heads, interpreting the data read from platters, and communicating with computers via an interface like SATA (serial ATA).

Hard disk drive formats 

Hard drive formatting doesn't refer to different physical formats like size or shape. Rather, it refers to the file system applied to the drive. The idea here is to prepare it for use with a specific file system. 

Windows supports NTFS, FAT32, and exFAT formats, with NTFS considered to be a more modern file system. If you have a Mac, you’ll use the APFS format. 

NTFS 

NTFS (New Technology File System) file format is the default option for Windows device users when formatting a primary drive. It is also ideal for external hard disk drives because it’s compatible with an array of devices. 

With support for files over 4 GB in size, you can transfer large files. The NTFS file system also includes file permissions, disk quotas, and encryption features for advanced security.

Most machines running the newest Windows versions use NTFS for partitions. 

FAT32

FAT32 (File Allocation Table 32) is the oldest yet remains the most common file system today, thanks to its usage in flash drives. It isn’t as efficient as NTFS, but works with a wide range of devices both old and new.

By comparison, it has a limited file size of up to 4GB and is only best for storing small files on removable storage. Users can run Windows from a USB drive using FAT32.

ExFAT

ExFAT (Extensible File Allocation Table) was optimized for flash storage like USB drives but works with hard disk drives as well. It offers better read and write compatibility across different operating systems than NTFS. An exFAT file system is the format you want to use for an external drive you plan to use on multiple devices.

Modern video game consoles, including the PlayStation 4, PlayStation 5, and Xbox One, use this file format. 

APFS

APFS (Apple File System) is a powerful drive format for Mac users. This format will work on any kind of hard drive, although it is designed with flash storage SSD in mind. 

A lot of Mac computers, be it a MacBook, MacBook Pro, iMac, iMac Pro, or Mac Mini, now come with SSDs. One of the notable features of APFS is its ability to share data between files.

When you duplicate a file on a system using APFS, the new copy doesn’t immediately consume additional storage space. Instead, APFS creates a reference to the original file.

How to completely wipe a hard disk drive

Formatting a hard drive for good so that the data cannot be recovered is an essential step to ensure your sensitive files are not accessible. Make sure you understand how to wipe a hard drive by reading the instructions below.

You may decide to format your hard drive for a variety of reasons. It could be time to install a new operating system like Windows onto a blank hard drive. Reusing your storage device is another obvious reason to erase all data beforehand. Those wanting to sell a drive will need to get rid of data, too. 

If your drive encounters errors, deleting it can do the trick. Luckily, there’s a safe way to make your data pretty much impossible to recover. Use Disk Utility for Mac or Disk Management for Windows.

Before you start, make sure to back up any important data to an external storage device—a USB drive comes in handy. A cloud storage solution is another great way to save your data. 

For Windows 10 and 11 using Disk Management

  1. Press the Windows + X keys and select Disk Management.
  2. Right-click on the drive you want to format and select Format.
  3. Choose a name for the drive and select a file system (like NTFS for Windows).
  4. Click OK to format the drive.

For macOS using Disk Utility

  1. Open Disk Utility (Applications > Utilities > Disk Utility).
  2. In the sidebar of Disk Utility, select the drive you want to erase. 
  3. Click on the Erase button in the toolbar.
  4. Select a file system format (like APFS for macOS 10.13 or later) and adjust your security options if available.
  5. Click Erase to confirm.

Simply deleting files doesn't necessarily mean the data is gone forever. The data may still be physically present on the drive and recoverable with data recovery software. You need to format it fifteen times for efficiency. 

Comparing hard disk drives to solid-state drives

Traditional hard disk drives are increasingly being replaced by solid-state drives (SSDs) in modern PCs. All tablets and smartphones also use a form of SSD. 

An SSD memory storage fulfills the same purpose as an HDD, only that it uses a more advanced technology.

The best computer setups use both HDDs and SSDs in one system. However, it still important to understand the difference between them. 

Hard disk drives (HDDs)Solid-state drives (SSDs)
Data storageStore your data on a magnetic diskDo not contain moving parts and instead store data on flash-memory chips
Storage capacity and costGenerally offer more storage capacity for much less moneyCome in smaller capacities for the price, but are catching up with HDDs
DurabilityMore susceptible to physical damage because of the spinning plattersMore durable as they lack moving parts, and can better withstand drops and bumps
Noise levelMake noise because of the spinning platters and the movement of the read-write headProduces less noise and heat due to the lack of mechanical movement. 
Processing capabilitiesDon’t process lots of data requests faster; HDD arms can only read one part of their magnetic disks at onceLoads and saves data faster for anyone who multitasks
SizeTend to be physically larger than SSDsTend to be smaller in size than HDDs

Frequently asked questions

What does a hard disk drive look like?

The outer casing of a hard drive protects the delicate internal components of a hard drive from microscopic dust. If you could see the device, it looks more like a stack of small phonographs. This is because virtually all mechanical hard disks are composed of a collection of platters. 

What data does a hard disk drive store? 

Simply put a hard drive stores data for later retrieval. It stores three types of data: operating systems (OS), such as Windows, applications like Google Chrome, and user-generated files. 

What are the most common form factors for HDDs?

They are 3.5-inch and 2.5-inch. The 3.5-inch drives are used in desktop computers and servers, while 2.5-inch drives are standard in laptops. 

Can I boot my computer without a hard drive?

No, because it is the device that stores an operating system. You can, however, start up your computer if you have an alternative bootable device, such as a USB flash drive.

Author

Written by Lizzy Schinkel & WhatIsMyIP.com® Editorial Contributors

Lizzy is a tech writer for WhatIsMyIP.com®, where she simplifies complex tech topics for readers of all levels. A Grove City College graduate with a bachelor’s degree in English, she’s been crafting clear and engaging content since 2020. When she’s not writing about IP addresses and online privacy, you’ll likely find her with a good book or exploring the latest tech trends.

Reviewer

Technically Reviewed by Brian Gilbert

Brian Gilbert is a tech enthusiast, network engineer, and lifelong problem solver with a knack for making complicated topics simple. As the overseer of WhatIsMyIP.com®, he combines decades of experience with a passion for helping others navigate the digital world.