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.
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 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.
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.
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.
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.
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.
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.