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What Is a Hard Drive?

Hard drive.
Hard disk drive with case removed to show the platters and the read-write head.
Disruptions to the hard drive's functioning can cause a computer to crash.
Thumb drives are small external drives that can expand the storage space of a computer.
An external hard drive.
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  • Originally Written By: Katharine Swan
  • Revised By: S. Gonzales
  • Edited By: O. Wallace
  • Last Modified Date: 09 October 2014
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A hard drive, also known as a hard disk drive (HDD), is a fundamental part of modern computers. Functioning as an internal storage device, it allows a computer to house and execute important files and programs, like the machine's operating system, and its components work together to actively seek, read, and write data on system and user-generated files. The delicate nature of the standard hard disk makes it susceptible to damage and data corruption or loss, however, and repairing or replacing one can be costly. Damage can often be avoided by minimizing the drive's exposure to environmental factors, like dust and rough-handling.

Internal Drives

There are two main types of hard drives: internal and external. The internal drive is the main storage area of a computer, and typically, the operating system as well as programs that are manually installed by the user are found here. Most computers designate it as the C drive, and program installation will occur on this primary partition by default. Modern computers often have several hundred gigabytes of storage, which provides enough room for the average user's collection of applications, documents and media throughout the computer's lifespan. An internal drive usually connects to the computer through either Parallel Advanced Technology (PATA), Serial ATA (SATA), or Small Computer System Interface (SCSI).

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External Drives

External drives are usually used to hold back-up copies of documents and programs, to store archived files, or to hold large data files that aren't used regularly, among other things. They usually don't include the operating system or any programs that are needed to make the computer work. Most connect to the machine through a USB or FireWire® connection, although some wireless models are also available. They are also sometimes called portable drives, since they can often easily be moved from one computer to another.

Memory Technology

A traditional hard drive uses similar memory storage technology to cassette and video tapes. Much like tapes, these drives contain round, mirror-like platters that are covered with a delicate, magnetic material. The platters are usually made of glass or aluminum, but they may appear shiny because of the polished magnetic material on their surfaces.

Just as the head inside of a cassette player or VCR reads the data on a tape, a head inside of a hard disk drive reads and writes data to platters. When it writes, the head causes changes the direction of the magnetic material on the platters to represent binary bits of data, which are saved and can then be read. Located on an arm next to the platters, the head pivots back and forth over them, constantly seeking or writing new information.

Internal Components

The average modern hard disk drive has several platters inside of it, stacked one on top of the other, like a sandwich cookie. A small gap between each platter allows the heads to pass over them. The heads rely on the same arm but have separate branches, much like the tines of a fork turned on its side.

When a computer is powered on, the platters immediately begin to spin. Those in a desktop computer's hard drive typically get up to about 7,200 rotations per minute (RPM), while the drives in laptop computers usually run at 5,400 RPM, though it is not uncommon to see high-end disks that reach 10,000 or even 15,000 RPM. When the drive's fan is not running, the steady hum of the spinning may be heard.

The platters continue to spin, even if no data retrieval or memory writing takes place. The arm only moves when a program runs, or a file is opened, saved, or deleted. During these processes, the arm can travel across the surface as many as 50 times in a single second. The head never actually touches the platters, but instead skims just above them, supported by a cushion of moving air that is generated by the spinning disks.

Solid State Drives

Although platter technology drives the majority of hard drives on the market, there are an increasing number of solid state drives (SSD) available. Instead of spinning disks, they contain no moving parts at all; data is stored on special computer chips instead. This technology allows the drive to read and write data more quickly, and the disks are not as susceptible to physical damage as regular hard drives, but they are typically much more expensive. With no moving parts, SSDs may have a longer lifespan than regular drives because there is no motor to burn out or arm to break. If the drive does fail, however, it may do so suddenly and without warning, and all data may be completely lost.

Hybrid Drives

There are also hybrid drives that combine a standard hard disk and an SSD. The platters in a hybrid don't spin constantly, and that part of the drive is only activated when needed. Data that is called on regularly is stored on the SSD, and only moved to the platters when that drive is full. This can mean faster boot times and computer performance at a lower price than using an SSD alone, but programs that require a lot of memory may not be any faster, since they'll rely on the traditional drive.

Common Problems

There are several ways that a standard hard drive's functionality can be compromised. The rapid motion and delicate maneuvering of platters and heads inside a disk make it susceptible to a "head crash," in which the heads touch the platters and damage the magnetic surfaces. Platters exposed to dust can cause a disk's arm to bounce as it operates, and spindles can become stuck, resulting in locked components. Bumping a computer or dropping it can cause electromagnetic damage, even if the machine has been turned off.

Repair and Replacement

Repairs on standard hard disk drives can be expensive, and they can even rival the cost of new, low-end computers. This work usually needs to be done by a professional, and opening the drive at home will typically ruin it and void any warranty. Many computer experts also recommend that novices not try to replace a broken drive at home because of the delicate magnetic properties of the disk and the high risk of damaging other electronic components inside the computer.

Avoiding Problems

There are certain things that a computer user can do to make a hard drive last longer. People should always handle any machine gently, as even abruptly moving a laptop could cause a head crash. It's best to move a computer that's turned on as little as possible, since a disk is more likely to be damaged while it is running. Although the drive is sealed, users should keep the entire machine as dust-free as possible, and make sure that the fan and any other cooling devices are clean and working correctly. Regularly backing up a computer's data on external hard drives, flash drives, or cloud storage services can protect users from losing important files if the drive does fail and needs to be repaired or replaced.

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Discuss this Article

amypollick
Post 28

@anon347639: Anywhere. Wal-Mart, KMart, Big Lots, the dollar store, Target, the checkout lines at the grocery store, any office supply store. Just look for them. They're everywhere. I've even seen them at truck stops.

anon347639
Post 27

Where can I get a cheap USB stick to store documents?

anon310719
Post 26

How do I download a movie to my PC hard drive?

anon300711
Post 25

Can someone help me? My hard disk drive doesn't want to work anymore, and my laptop has been telling me to replace it or whatever, but what I want to know is that if my laptop needs to have a certain specific hard drive or does it not matter?

sk8erboy225
Post 20

OK, so I started up my laptop yesterday and it said start with something. I forget so I ignored it like a noob, but a few hours later my laptop crashed on me and I was like what? So I don't know if something is wrong with the hard drive or my laptop is just derp but I am a nerd in training so a little help would be nice.

anon105975
Post 15

Where can I purchase an external usb disc drive? Is it the same as a hard drive?

anon72318
Post 14

what's the compatible hard drive for a apple g4 power mac desktop? please specify the brand also.

anon51467
Post 12

Dose anyone know what sort of hard drive would be good for a notebook, computer, interactive whiteboard please?

anon48066
Post 10

anon31482 there is not really any good features to a hard drive. i had mine in an open case so you could see the fork writing on the platter.

anon31482
Post 8

Does anyone know any good features of the hard drive?

crazysugarc
Post 2

when my computer comes on it says it can't find certain drives. this been going on since i had it cleaned now my cd burner and printer not working any suggestions?

sarix
Post 1

An error showed up when starting my laptop, I ran a check disk but it said that there were problems in the hard drive that could not be fixed. I am thinking in buying an enclosure to insert the hardrive and be able to recover some of the files, will these work?

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