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What is a hard disk drive (HDD)?

A computer hard drive (or a hard disk or HDD) is one kind of technology that stores the operating system, applications, and data files such a documents, pictures and music that your computer uses. The rest of the components in your computer work together to show you the applications and files stored on your hard drive.

How does a hard drive work?

A hard disk drive (HDD) is composed of a platter that contains compartments to hold data. This data is your operating system, applications, and any files you have created. There is also an accuator arm that moves across the platter to read or write the information requested. To make this process faster, the platter spins as the accuator arm moves across it.

The compartments that hold the data can be spread out all over the hard disk. That is, data is not written sequentially. There is an indexing system to allow the accuator arm to find all of the pertinent data.

The platter and the accuator arm are delicate, so they are covered by a steel case. This prevents damage to the disk under normal circumstances.

A hard drive

What are the advantages and disadvantages of a hard drive?

HDDs are proven technology that can hold a large amount of data (this varies by the size of the drive) and are relatively cheap. Under normal use, they are reasonably durable and function well.

There are drawbacks, however. Hard disk drives can be slow, especially to open large applications or files. Because they do not write data sequentially, the data can become fragmented, with empty space within each compartment. This empty space is too small to use for data, but when the empty space is added together it can take up a large portion of the drive. Learn how to defragment your hard drive.

Hard drives use a lot of power and produce a lot of heat. This makes them less useful in smaller computers like laptops and notebooks. Under normal circumstances HDDs are durable. But when hard drives are in portable computers that can be dropped or bumped while the platter is spinning, the drive can be damaged so that the data on them is not retrievable by end users.

What is an external hard drive?

An external storage drive is a separate device that attaches to a computer, generally through a USB port. Though it does not replace the need for an internal drive, an external drive gives you more storage space for backup files, pictures, music, and more.

External drives are also portable; you can move them between computers. This will allow you to share things like pictures more easily.

What are the differences between internal and external hard drives?

Your computer must have at least one storage drive to function. Usually, the storage drive is an internal drive; located inside the computer case. Internal drives come in a variety of storage sizes and can be replaced if you don't have enough storage space.

You can set up a computer with an external drive in addition to the internal drive. An external drive attaches to the computer, generally through a USB port. An external drive gives you more storage space for backup files, pictures, music, or particularly large files.

External drives are also portable; you can move them between computers. This will allow you to share things like pictures more easily.

An external hard drive

What are the other memory storage options?

Hard disk drives are only one kind of storage drive. Solid state drives (SSDs) are storage drives that perform the same functions as hard drives. SSDs use a different kind of technology from HDDs, more like the technology in a USB thumb drive. This technology uses less power and produces less heat. SSDs also have no moving parts, so are more durable in portable applications. Learn more about the benefits of a solid state drive here.

Solid state drives are now standard in most laptops and other portable computers. You can easily change an existing HDD to an SSD yourself. The Crucial® Advisor™ tool or System Scanner tool can help you find the right SSD for your computer.


Every computer needs at least one storage drive to hold the operating system, applications, and data files. Many storage drives are hard disk drives, but there is another option. Adding an external storage drive is an easy way to expand your storage capabilities.


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