Hard disk drive
Hard disk drive (HDD), hard drive, hard drive or hard disk [b] is the storage of data used to store and retrieve digital information using one or more rigid device ("hard") rapidly rotating discs (disks) coated material magnetism. Dishes are combined with magnetic heads arranged in the arm moves the engine, that read and write data on the surfaces of the plate.  to access data from a form of RAM, and this means that the individual blocks of data may be stored or retrieved in order, rather than sequentially. Hard drive retains its data even when the power is.
Introduced by IBM in 1956 , and has become a solid secondary storage device dominant for personal computers in the 1960s consumer drives early, maintained continuous improvement, HDD this position in the modern personal computers and servers era. More than 200 companies have produced hard disks, although most of the current manufacturing drives Seagate, Toshiba and Western Digital. The revenue of disk storage in the worldwide $ 32 billion in 2013, up 3% from 2012. 
The main characteristics of the hard drive is their ability and performance. Ability referred to in similar units of prefixes to the authorities in 1000: January 1 terabyte (TB) has a capacity of 1000 GB hard (GB; where GB = 1 billion bytes). Usually, part of the hard drive is available for the user capacity, because it is used by the file system and the operating system for your computer, and can be built redundancy for error correction and recovery. Performance is the time to move the capital to the (average access) of the track or cylinder as well as the time it takes required for the sector to move under the head (average latency, which are based on the physical rotation speed in rpm), and finally, and the speed with which data (data quickly) is sent.
Two factors most common way modern hard drives 3.5-inch desktop PC, and 2.5 inches, primarily for laptops. Standard interface is connected HDD cable systems engines such as Serial ATA (SATA), USB or SAS (Serial Attached SCSI) cable.
From 2015, the main rival to secondary storage technology is a flash memory in the form of solid-state disks (SSD), but hard drives are still the primary means for storing secondary benefits because of price per volume and recording capacity.   However, hard drives are replaced with hard drives in terms of speed, power consumption and durability are the most important considerations.