What is a hard drive? Everything you should know about the computer storage device

  • A hard drive, also known as a hard disk drive, is a storage device used on many computers. 
  • A hard drive consists of spinning platters that store digital information read by fast-moving read/write heads.
  • Hard drives are the computer component most prone to failure but offer high performance for the price.  
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A hard drive is a critical component of many computers. The device stores your programs and data regardless of whether your PC is turned on or off. It's considered semi-permanent storage because while any data on a hard drive should last for years without failure, no digital storage system is perfect or permanent.

Here's what you need to know about hard drives. 

How hard drives work on a computer 

A hard drive traditionally uses a set of spinning metal platters. Each platter has a head that moves rapidly back and forth across the platter, using magnets to read or write data as needed. While it needs to be completely sealed inside the hard drive housing to protect the platter from even microscopic dust, if you could see the hard drive, it would resemble little more than a tiny phonograph player, complete with tonearm. 

Perhaps more accurately, a hard drive would look like a stack of small phonographs because virtually all hard drives are composed of a set of platters. Each platter can only hold so much data, so hard drive manufacturers increase capacity by stacking platters in the same drive. 

It's worth noting that while this description accurately describes a hard disk drive (HDD), people often refer to solid-state drives (SSDs) as hard drives as well. So while as a general rule, a hard drive is a mechanical storage device that relies on a spinning platter, informally, a hard drive can mean an HDD or an SSD.

Increasingly, SSDs are completely replacing HDDs in computers, so it is increasingly difficult to find a traditional hard disk drive in a modern PC.

Hard drive advantages and disadvantages

First and foremost, a hard drive is a relic of an earlier age, when the best way to store massive amounts of data was to use a mechanical system with moving parts. The hard drive is virtually the only moving part left in modern computers (aside from laptop hinges and power buttons). That makes it the most likely component to fail, with a dramatically shorter mean time between failure (MTBF) than any other part of a computer, bar none. 

It's sometimes worth the risk, though. A hard drive can store a lot of data at a very low cost, which typically adds up to a low price-to-performance ratio. A hard drive's lifespan is also "good enough" for most situations since it's typically measured in years. For more information, read our article on how hard disk drives compare to solid state drives.

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