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At least 218 companies have manufactured hard disk drives (HDDs) since 1956. Most of that industry has vanished through bankruptcy or mergers and acquisitions. None of the first several entrants (including IBM, who invented the HDD) continue in the industry today.
Circuit board of a 2.5-inch Samsung hard disk MP0402H. A typical HDD has two electric motors: a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place.
Hard disk drives store data in the magnetic polarization of small patches of the surface coating on a disk. The maximum areal density is defined by the size of the magnetic particles in the surface, as well as the size of the "head" used to read and write the data. In 1956 the first hard drive, the IBM 350, had an areal density of 2,000 bit/in 2.
Hard disk Seagate Barracuda 1500 GB, 3.5 inch, capacity 1.5 TB, built 2011. The head unload ramp is the orange plastic piece on the right edge of the drive. Available in capacities between 2 TB and 3 TB (XT) with 64 MB cache, 1 TB and 2 TB (LP) with 16 MB or 32 MB cache, 1 TB, 1.5 TB and 2 TB (Green) with 16 MB to 64 MB cache depending on model.
Hard disk drive (HDD) Price per capacity SSDs are generally more expensive than HDDs and are expected to remain so. As of early 2018, SSD prices were around $0.30 per gigabyte for 4 TB models. [23] HDDs, as of early 2018, were priced around $0.02 to $0.03 per gigabyte for 1 TB models. [23] Storage capacity
A 500 GB Western Digital hard disk drive with a 16 MB buffer In computer storage , a disk buffer (often ambiguously called a disk cache or a cache buffer ) is the embedded memory in a hard disk drive (HDD) or solid-state drive (SSD) acting as a buffer between the rest of the computer and the physical hard disk platter or flash memory that is ...
Enhanced Small Disk Interface (ESDI) was an attempt to minimize controller design time by supporting multiple data rates with a standard data encoding scheme; this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives were not downward compatible (i.e. a 15 or 20 ...
2.5-inch hard disk drives often consume less power than larger ones. [12] [13] Low capacity solid-state drives have no moving parts and consume less power than hard disks. [14] [15] [16] Also, memory may use more power than hard disks. [16] Large caches, which are used to avoid hitting the memory wall, may also consume a large amount of power.