“A rigid non-removable magnetic disk with a large data storage capacity.”

There are several different types of hard drives for storing software and data files: hard disk drives, solid-state drives and external drives. Learn about how they work and how to select the right drive for a particular computer system.




You may have experienced this scenario: you turn on your computer and you get a black screen with the message ‘Imminent Hard Disk Failure’. Or you’ve dropped your laptop on the floor, your screen goes black and your computer won’t turn back on again. More often than not the problem is your hard drive. If your hard drive has crashed, you may have lost all your documents, photos, music, etc. It can be one of the more frustrating experiences for any computer user. Read on to learn how your hard drive works, and some simple steps you can take to avoid losing all your files if it crashes.


There are two general types of hard drives:


  1. hard disk drives

    (HDD):,which use one or more rotating discs and rely on magnetic storage, and


  1. Solid-state drives

    (SDD):, which have no moving mechanical parts but use flash memory like the kind found in USB flash drives.



Hard disk drives (HDD):

Hard disk drives have been the dominant type of storage since the early days of computers. A hard disk drive consists of a rigid disc made with non-magnetic material which is coated with a thin layer of magnetic material. Data is stored by magnetizing this thin film. The disk spins at high speed and a magnetic head mounted on a moving arm is used to read and write data. A typical hard disk drive operates at a speed of 7,200 rpm (rotations per minute), so you will often see this number as part of the technical specifications of a computer. The spinning of the disk is also the source of the humming noise of a computer, although most modern hard disk drives are fairly quiet.


 In general, hard disk drives are very robust and can be used for many years without problems. However, hard disk drives can fail and one of the most common reasons is a head crash. This occurs when the magnetic head scratches the magnetic film. This typically happens as a result of a physical shock, like dropping a computer while it is on. When your hard drives experiences mechanical failure you can often hear a grinding or scratching sound. Such as crash results in data loss since the magnetic film gets damaged. It is therefore always a good idea to have a backup copy of the important files on your hard drive.


Solid-state drives (SDD):

Solid-state drives (SDD) are a relatively new alternative to more traditional hard disk drives. Solid-state drives do not have moving parts, and data is stored electrically instead of magnetically. Most solid-state drives use flash memory, which is also used in memory cards for digital cameras and USB flash drives. Since there are no moving parts, solid-state drives are much less vulnerable to damage from physical shock. The major downside of solid-state drives is that they are a lot more expensive than hard disk drives, although prices are gradually coming down.


Despite the cost, solid-state drives are quickly becoming the preferred type of hard drive for certain types of computers because they are very damage proof and smaller than regular hard disk drives. For example, the MacBook Air now comes standard with a solid-state drive using flash memory.



Capacity and performance:

The most important characteristic of a hard drive is how much data it can store, referred to as the storage capacity. A typical internal hard drive for a new desktop computer or laptop has a storage capacity of several hundred gigabytes (GB) up to 1 terabyte (TB). How large is a terabyte? Consider that a typical song in MP3 format is in the order of 5 to 10 MB. You could store approximately 150,000 songs on a 1 TB drive.


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