hard disk

(redirected from Hard disks)
Also found in: Dictionary, Thesaurus, Medical, Financial.

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

(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 ?
From above mathematical expressions, we know that even if two data points are lost (two hard disks damaged), we can figure out their exact values (data recovery) by making use of remnant data (undamaged hard disks).
After you're up and running Windows 98 gives you the option of converting all your files--applications and data--to a format that will save space on your hard disk and speed applications.
PCMCIA card readers are now available from several companies which allow the Type III hard disk to be used in desk-bound PCs.
It is usually easier to leave some of the data on the computer's hard disks, even if it can be inappropriately accessed.
Instead of wasting time accessing the flower hard disk repeatedly for the latest data, cache memory is able to dish it up quickly.
Although tape remains one of the least expensive storage mediums--costing as little as a tenth of a cent per megabyte of stored data--it's frustratingly slow compared with hard disks or floppies.
KOMworx Hard Disk Archiving solution in combination with the EqualLogic iSCSI SAN solution and Microsoft's Simple SAN initiative is an innovative collaboration to bring the best of storage technology to the small and medium business market," said Babar Khan, Director of Marketing, KOM Networks.
Once a connection is made, the remote host computer flashes a silent command back to the stolen portable that automatically erases its hard disk and then disconnects.
Disk caches improve the data transfer rate, or the rate at which data from the hard disk are routed into the processor.
com/reports/c25947) has announced the addition of Portable Hard Disk Storage to their offering.
The Disk Jockey is a revolutionary new hard disk copy, backup and diagnostic tool that allows users to copy data between hard disk drives at lightning fast speeds while maintaining the attributes of the original hard disk, including hidden folders and operating system files.