hard disk


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hard disk

a disk of rigid magnetizable material that is used to store data for computers: it is permanently mounted in its disk drive and usually has a storage capacity of a few gigabytes

hard disk

[′härd ¦disk]
(computer science)
A magnetic disk made of rigid material, providing high-capacity random-access storage.

hard disk

(storage)
(In contrast to floppy disk) A magnetic disk data storage device where the disks are rigid and fixed to a central axle. They are usually packaged with associated read/write heads and electronics. Most hard disks are permanently connected to the drive (fixed disks) though there are also removable hard disks.

See magnetic disk.

hard disk

The primary computer storage medium, which is made of one or more aluminum or glass platters, coated with a ferromagnetic material. Although the terms "hard disk" and "hard drive" are used synonymously; technically, the disk spins inside the drive.

All computers have an internal hard disk for storage, and hard disks in external cases can be plugged into a USB, FireWire or eSATA port for additional storage. Slowly but surely however, hard disks are being replaced by non-mechanical drives (see solid state drive).

Today's hard disks are "fixed," which means their platters reside permanently in the drive. In the past, removable cartridges were used for backup and transport (see removable disk).

Storage... Not Memory
Hard disks are not the computer's main memory. Disks store programs and data until deliberately deleted by the user, but memory is a temporary workspace. To learn how this workspace is used to process data, see memory. For a summary of memory and storage types, see storage vs. memory.

Capacity and Speed
Hard disks rotate constantly from 4,000 to 15,000 RPM; however, to preserve battery or power, they can be configured by the user to turn off after a defined period of inactivity. Capacity is measured in bytes, and the largest drives have passed the terabyte threshold.

Speed is measured by how long it takes to begin transferring data; approximately three to 15 milliseconds (by comparison, CDs/DVDs take 80 to 120 ms) and the rate of transfer is measured in hundreds of megabytes per second. See hard drive capacity, access time and transfer rate.

Hard disks are pre-formatted at the factory, which divides the platters into identifiable sectors. For more details on disk structure, see magnetic disk, format program, hard disk defect management and drop protection.

Hard Disk Types
Over the years, several kinds of hard disks have been employed. Today, SATA drives are the most common, although SAS drives are also used. For more details, see SATA, SAS, SCSI and hard disk interfaces.


Non-Removable Internal Hard Disk
Hard disks use one or more metal or glass platters covered with a magnetic coating. In this drawing, the cover is removed.







First Hard Disk (5MB)
Part computer, part tabulator, in 1956, IBM's RAMAC was the first machine with a hard disk, which was extraordinary technology at that time. Each of its 50 platters two feet in diameter held a whopping 100,000 characters, the total equivalent to five megabytes today. (Images courtesy of IBM.)


First Hard Disk (5MB)
Part computer, part tabulator, in 1956, IBM's RAMAC was the first machine with a hard disk, which was extraordinary technology at that time. Each of its 50 platters two feet in diameter held a whopping 100,000 characters, the total equivalent to five megabytes today. (Images courtesy of IBM.)







First Personal Computer Hard Disk (5MB)
A fraction of the RAMAC's size, Seagate introduced the first hard disk with 5.25" platters in 1979. Today's platters are 3.5" for desktops and 2.5" for laptops. See ST506. (Image courtesy of Seagate Technology, Inc.)







Four Decades Later
Much less than entry level these days, but in 1998, this Seagate drive's 47GB was impressive. Four decades of development after the RAMAC let us store 100,000 times as much data on the same surface. All this is one platter today. (Image courtesy of Seagate Technology, Inc.)







World's Smallest Hard Drive
The size of a postage stamp, Toshiba introduced a 0.85" hard drive for mobile devices and shipped 2GB and 4GB units in 2005 and 8GB in 2007. However, solid state USB drives have long surpassed 8GB. (Image courtesy of Toshiba Corporation.)
References in periodicals archive ?
Table Product Specifications of Hard Disk Drives Figure Global Sales Market Share of Hard Disk Drives by Product Types in 2014 Figure Global Sales Market Share of Hard Disk Drives by Applications in 2014 Table Manufacturing Cost Structure Analysis of Hard Disk Drives in 2014 Figure Manufacturing Process Analysis of Hard Disk Drives Table Capacity (K Units) and Commercial Production Date of Global Hard Disk Drives Key Manufacturers in 2014 Table Global Production of Hard Disk Drives by Regions 2010-2015 (K Units)
Newer hard disks and RAID 6 chip accelerators are laying the foundation for RAID 6 technologies to deliver the next stage in data protection.
I usually upgrade computers because they have become too slow or restricted in RAM or hard disk space, but back then, reliable disk compression utilities were not available.
Data is not kept on computer hard disks and is erased from those hard disks in a special way if it is ever stored there even on a temporary basis.
They serve many different functions: fax/modems, solid-state hard disks, local area network (LAN) adapters, sound generators and many more.
Like hard disk drives, magnetic tape is inherently rewritable, making data authentication difficult and forestalling acceptance by key regulatory agencies.
A 20-Mb file, for example, will take only about 10 Mb of space on your hard disk.
Micro hard disks will be advantageous in the 4GB-above market in the next three years.
com: Virtual tape is the use of a special storage device that manages less-frequently needed data so that it appears to be stored entirely on tape cartridges when some parts of it may actually be located in faster, hard disk storage.
In such a case, although a hard disk failure message appears on the screen when the user turns on the computer, the user has no way of knowing the original disk was stolen.
5" external hard disk drives with capacities of up to 250GB and 320GB.