A hard disk drive is a non-volatile data storage device within a computer and permanently stores data on a computer that can be retrieved by the system that is sometimes abbreviated as a hard drive, HD or HDD.
The hard drive was originally produced by IBM in 1956 with a storage capacity of 5MB (megabyte) and cost around $50k. The hard drive was built into the computer that contained it and was not removable.
IBM then introduced the first removable hard drive in 1963 with a 2.6MB capacity, by 1980 that capacity had increased to 1GB (gigabyte), though it weighed 550 lbs and cost $40k.
In 1992 Seagate introduced the first drive to spin at 7,200 RPM, later increased to 10,000 RPM in 1997 and 15,000 RPM in 2000.
A hard drive has an air tight casing and contains one or more platters that consist of circular discs with a magnetron coating that allows data to be stored to them. A desktop computer hard drive contains metal platters, whereas a laptop hard drive contains glass platters.
A hard drive is often capable of storing larger amounts of data than other types of storage devices, however, the actual size can vary.
Older hard drives may be limited to several hundred Megabytes (MB), whereas newer hard drives are frequently now several terabytes (TB). The introduction of new technology allows hard drives to increase in storage capacity.
The external case size of the hard drive differs depending upon the type of computer it is designed to be contained in. A 3.5″ hard drive is normally stored within a desktop computer and a 2.5″ hard drive is normally located within a laptop computer.
Hard Drive Speeds
The speed of a hard drive can also differ. This is the speed at which the platters within the drive actually spin, the faster they spin, the more quickly the data present can be read and written to them.
It is possible to find drives that spin at upto 15,000 RPM (revolutions per minute), however most hard drives rotate and either 5,400 RPM or 7,200 RPM.
Hard drives that spin at 7,200 RPM offer faster read and write speeds than 5,400 RPM hard drives, meaning that they can open and transfer files more quickly, however, they are more expensive and also make more noise and generate more heat.
They can also have a shorter lifespan than 5,400 RPM hard drives. These types of hard drive are best suited to being used as primary drives that contain the operating system.
The 5,400 RPM hard drives offer slower read and write speed but are cheaper, use less power and are therefore quieter and generate less heat. This makes them a good solution for secondary storage backup hard drives that are not frequently accessed.
Though 7,200 RPM hard drives are faster than 5,400 RPM drives, they are only around 20% faster, with the 7,200 offering an average read and write of 120 MB/s and the 5,400 RPM offering an average of 100 MB/s.
Location of a Hard Drive
Internal hard drives are located within a drive bay and are connected to the motherboard via a data cable. That data cable is normally a SATA (abbreviation of serial AT Attachment) type, however, older and slower type cables consist of ATA (AT Attachment) and SCSI (Small Computer System Interface).
The internal hard drive also connects to a power source supplied by the Power Supply Unit (PSU) contained within the computer casing.
The hard drives are used to permanently store data including the operating system that is required for the computer to function as well as the personal files of the user, such as digital camera photographs, emails and documents. Without the hard drive, the computer cannot function.
Components of a Hard Drive
A desktop hard drive contains a spindle, head actuator, read/write actuator arm, platter and a read/write head. The rear of the hard drive contains a disk controller that is a main circuit board that allows the hard drive to connect and communicate with the computer.
Type of Data Stored to a Hard Drive
Any data can be stored to a hard drive, including any operating system and software files required to make the computer function and all user files, such as downloaded files, photographs, emails, documents and music.
The Method of Access and Storage of Data on a Hard Drive
The disk controller sends and reads data from the hard drive. When the operating system of a computer needs a file, it identifies the location of that file on the hard drive through the operating systems own file allocation table and then instructs the hard drive actuator to direct the read/write arm and head to that location.
As files are often located in different places on a hard drive, the head often needs to move to different locations in order to read all of the information required.
All data stored to a hard drive is through magnet and, in order to read the data at the particular point on the hard drive, all of the data present is either stored as a 0 or a 1, on one side the magnetic polarity is 0 and the other 1. The hard drive reads this as binary data and can understand what data is on the hard drive.
Internal hard drives
Computers contain internal hard drives that include the operating system that makes the computer work.
However, another type of hard drive is the external drive that can be connected to the computer via a cable connection, normally a USB, FireWire or eSATA and can be used to backup data from the computer.
An external hard drive is normally stored within an enclosure to prevent damage to the drive and data contained on it.
An external hard drive can be contained within a large or small enclosure and some enclosures can contain multiple hard drives connected together through a circuit board within the casing.
External hard drives can allow a user to store more files and folders than can be stored on the space available within the computer and are frequently used to store backup data.
Solid State Drives (SSD)
Whilst hard drives contain solid platters within them that spin at over 5,400 RPM, solid state drives have begun to replace them as, though they are more expensive, they offer faster access times and less heat and better reliability.
Solid state drives were introduced by Sandisk in 1991 and had a storage capacity of 20MB.
Instead of magnetic platters, these drives use circuit assemblies as memory in order to store persistent data.
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