A hard drive in a computer is an internal or external device that stores data such as operating systems, applications and user files. You may also have come across the term HDD. HDD is a common abbreviation that stands for Hard Disk Drive. HDDs are non-volatile storage devices, meaning they retain stored data even when power isn't being supplied. 

How does a hard drive work?

An HDD includes two main elements: a spinning platter and an actuator arm. 

  • The spinning platter is a circular magnetic disk containing tracks and sectors that retain data. The disk platter is rigid, unlike the flexible medium used in floppy disks, which is why the device is called a hard disk drive.
  • The actuator arm moves across the radius of the spinning platter to read and write data. 

The actuator arm and platter follow the same basic principles of a vinyl record, but in a far more advanced way. 

A vinyl record contains only a handful of tracks on its surface, while a modern hard disk may contain 500,000 tracks on each side. Hard disks can also spin up to 15,000 rpm, while records only spin up to 78 rpm. Finally, the read head on the actuator arm acts like the needle on a vinyl record player, following the tracks on the disk. Unlike a record player needle though, the read head doesn’t make contact with the tracks, but instead hovers over the surface of the disk at extremely small distances, less than 10 nanometers. In comparison, a red blood cell is about 7,000 nanometers thick, and a human hair can be 100,000 nanometers thick.  

The tracks on an HDD are divided evenly into sectors, and each sector can store a fixed amount of data. As data is written to the hard drive, it’s laid out into these sectors. When a hard drive has been wiped clean or is new, this information can be laid out sequentially, which means it’s very efficient for the computer to read the data again in the future since it’s all in one place.  

Over time, as data is deleted or moved, the information is stored in fragments instead of sequentially, which means the actuator arm has to move around the disk surface more often as it hunts for information. This can lead to slower performance, but it’s possible to defrag a hard drive, and reorganize how the data is stored to make it more efficient again. 

Instead of an HDD, newer computers are usually fitted with an SSD (solid state drive). SSDs don’t need to be defragged, as the location of data doesn’t affect their retrieval times.  

What does a hard disk drive look like?

Because the platter and the actuator arm are delicate physical mechanisms, a solid case covers them to prevent damage under normal use. The hard drive cover will look like a metal box, and it will be clearly labeled as a hard disk drive or HDD. 

Here's what an internal HDD looks like beneath its metal casing. You can see the spinning platter and the actuator arm, and how they work together to read and write the data upon request.

A hard drive

Underneath the platter, you will also find circuitry and chips that control the components, and memory chips which provide a buffer to assist in reading or writing data to the drive.  

Internal vs external hard drives

Hard drives can be used both inside and outside computers. Internal hard drives are installed inside the computer's case and are directly connected to the motherboard and power supply. External hard drives are housed in their own enclosure and connect to a computer via USB, Thunderbolt or other interfaces. Internal drives are typically used for primary storage, while external drives are often used for additional storage, backups or transferring data between devices.  

How to improve hard disk performance

As your HDD ages, you may start to experience HDD lagging, with slow startups and longer load times.   

You can help prevent these slowdowns by occasionally doing a little maintenance work. Follow these steps to immediately improve performance. 

Defrag your hard disk drive

 Defragging your HDD reorganizes the data to store it sequentially, which leads to faster read times. 

Delete temporary files

Programs and apps can store temporary data that’s unnecessary and can take up a lot of storage space on your drive. To delete this data and free up space on your HDD, follow these steps. Depending on what Windows version you’re using, these steps may be slightly different. 

  1. In the search box on the taskbar, type disk cleanup, and select Disk Cleanup
  2. Select the drive you want to clean up and select OK.
  3. Under Files to delete, select the file types you want to remove. You can also select a file type to read a description of what it is. 
  4. Select OK when you have made your selections. 

Remove unnecessary data

Freeing space is a great way to improve storage performance. This could be deleting old programs and apps you no longer use or moving photos, videos and games over to an external storage device until you need them. Follow these steps to remove apps and programs. Steps may differ slightly depending on the Windows version you’re using. 

  1. In the search box on the taskbar, type programs, and select Add or remove programs
  2. Select the programs you want to delete. 
  3. Then select Remove

Enable write caching

This step enables the volatile memory (RAM) to collect data in a cache before writing it to the storage device. The cache can process the data faster, resulting in faster load times. Again, these steps may differ depending on the Windows version you're using. Here’s how to do it on Windows 10 and Windows 11. 

  1. Right-click the Start button.  
  2. From the menu, click Device Manager.
  3. Expand Disk Drives
  4. Right-click the drive where you want to turn on disk write caching, then click Properties
  5. Click the Policies tab. 
  6. Under Write-caching policy, check Enable write caching on the device
  7. Click OK to apply the changes. 

Upgrade your storage

The quickest way to improve performance is to upgrade to an SSD (solid state drive), which we'll talk about in the next section. 

Other memory storage options

Solid State Drives (SSDs)

You now have a good idea of how HDDs work, but there's also a new generation of computer storage available – SSDs.  

SSDs are storage drives that fulfill the same purpose as an HDD, only using a more advanced technology. 

What is the difference between an SSD and an HDD?

The benefits of an SSD include: 

  • Less power consumption
  • Less heat production 
  • Increased durability 

Upgrading to an SSD helps boost the performance of your PC or laptop, but one thing to consider when doing so is compatibility.     

SSDs come in different forms, whether that be SATA or NVMe. SATA drives are slower than NVMe drives but are more compatible with older machines. The Crucial® Upgrade Selector or System Scanner can help you find the right storage drive for your computer. 

If you’d like to learn more about the differences between SSDs and HDDs, check out our article comparing SSDs and HDDs

External storage

If you want to increase your data capacity without replacing your internal hard disk, adding an external storage drive is a quick and easy way to expand your storage capabilities. 

FAQs for hard disk drives

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