What is a Hard Disk? – Hard disk drive – Hard Disk Definition | computing
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What is Hard Disk?
A hard disk drive (hard disk), hard disk, hard disk, or fixe disk [b] is an electromechanical data storage device that uses magnetic storage and a high-speed hard disk plate of one or more magnetic materials to store and retrieve digital data. It is cover in red.
.. The composition is usually made of magnetic heads place on a moving mat that reads and writes information on the surface of the plate.  The data can be accesse randomly.
That is, individual blocks of data can be save and retrieve in any order. HDD is a type of non-food storage that retains store data even when it is close. ] ] ] Modern hard drives often look like small rectangular boxes.
Introduce by IBM in 1965, the ] HDD was a large secondary storage device for general-purpose computers that began in the early 1960s. Mass has been manufacturing personal computer devices, but HDDs maintain this position in the era of servers and personal computers. Mobile phones and tablets rely on flash memory storage devices.
More than 224 companies have manufacture hard drives to date, but after extensive industry integration, most drives were manufacture by Seagate, Toshiba and Western Digital.
Hard drives dominate the storage volumes generate for the server (exabytes per year). Production is growing slowly (transportation per acre ), but solid drive drives (SSDs) have high data rates, site storage density, reliability , and delays. Sales and vehicle shipments are declining because there are so few. And accessibility. Times    
what is hard disk in computer:
Revenues from SSDs, which mostly use NAND flash memory, are slightly higher than HDDs.
 Flash storage products more than double hard drive revenue in 2017.  SSDs cost 4-9 times per bit, but   replace HDDs in applications where , power consumption, small size, large capacity, and durability are important.   The bit cost of SSD has decrease, and the price premium has decrease compare to HDD. 
The two most common form factors for modern hard drives are 3.5 inches for desktops and 2.5 inches for laptops in particular. Hard drives are connect to the system using standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB, or SAS (Serial ATA) cables.
History of Hard Disk:
The first production IBM hard disk drive, 350 disk storage, was move in 1957 as part of the IBM 305 Ramak system. Having a single hand with two reading / writing heads (one face and the other face down), moves horizontally between the adjacent dominance pair and the platter pair and moves to the second set, respectively.    The IBM 350 variants were the IBM 355, IBM 7300, and IBM 1405.
In 1961, IBM introduce the IBM 1301 disk storage unit , which replace the IBM 350 and similar drives, and move in 1962. The 1301 is made up of one (for Model 1) or two (for Model 2) indices, each with 25 plates, each plate approximately 1-8 inches (3.2 mm) thick.
The diameter is 24 inches (610 mm). ]] Previous IBM disk drives use only two read or write heads in each hand, while the 1301 use one type of 48 [e] heads (combs) each containing a single unit.
As move horizontally, and one head use surface. The cylinder position supports the read / write operation and the head flies about 250 microinches (approximately 6 µm) above the plate surface.
The head movement relies on a two-solar additional system for hydraulic actuators to ensure repetitive positioning. The 1301 cabinet is about the same size as the three-side refrigerators by the house, equivalent to about 21 million 8-bit bytes in each model. Access time was about a quarter.
Also in 1962, IBM introduce the 1311 disk drive model. It was about the same size as a washing machine and had 2 million crates in a removable disc bag. Users can purchase additional packages, such as magnetic island rails, and place them as need\
types of hard disk:
In 1963, IBM announce the 1302 , which double the 1301 track capacity and double the number of tracks per cylinder. The 1302 has one (for model 1) or two (for model 2) models, each with a separate flywheel. The first 220 tracks and the last 260 tracks.
Some high performance HDDs are produce with one head on each truck. For example, like the Burrows B-475 in 1964 and the IBM 2305 in 1970, the truck lost the time to move the physical head, and the waiting time was just the desire time. A block of information that changes to the position below the head.
 fixe] Known as a fixe head or any track disk drive in the head, these are very expensive and no longer in production.  42]
In 1973, IBM introduce a new type of HDD, calle the “Winchester”. Its main feature is that the disk head was not completely remove from the disk plate when the drive was close. Instead, the head can “land” a specific area of the disk surface during the spindown and then “take up” when the disk was moving.
This significantly reduce the cost of the head operating mechanism, but it was not possible to simply remove the disk from the disk, as was done with disk packs at the time. Instead, the first model of the “Winchester Technology” drive introduce a removable disc model that include both a disc pack and a head assembly, leaving the operating car in the drive when remove.
Later, “Winchester” Drive abandone removable media communication and returne to non-removable.
what is hard drive:
In 1974, IBM introduce the Swingram superintendent. This is possible because the Winchester record head works well when tilte to the recorde track.
The simple design of the IBM GV (Glover) drive , inventeby IBM’s Horsely Labs in England, became IBM’s most widely adopte electro-mechanical invention , and operators and filtering systems were finally introduc in the 1980s. Everyone was create. HDDs, and nearly 40 years and still global after 10 billion weapons.
Like the first removable pack drive, the first “Winchester” drive use a 14-inch (360 mm) diameter plate. In 1978, IBM introduce the IBM 0680 (Piccolo) swingarm drive with an 8-inch plate, describing the potential of small platforms that offer benefits.
This is follow by another 8-inch drive, follow by a 5 + 1⁄4-inch (130 mm) drive, measuring to replace the current floppy disk drive. The latter was first target at the then-emerging personal computer (PC) market.
During this period, powerful rare earth magnetic materials have become cheaper, complementing the design of the swingarm actuator and activating the HDD compact form factor.