hard disk drive

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hard disk drive

(storage)

(HDD) A disk drive used to read and write hard disks.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

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 used to have an internal hard disk for storage; however, today, storage can be solid state (see SSD). External hard disks can be plugged into USB or a eSATA port for more storage.

Hard disks are "fixed disks," which means the platters reside permanently in the drive. In the past, removable cartridges for backup and transport contained the platters (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 (RAM) 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
Capacity is measured in bytes, and the largest drives hold up to 10 terabytes. Speed is measured by transfer rate in megabytes per second as well as latency: how long it takes to begin transferring data, typically 3 to 15 milliseconds (ms). By comparison, CDs/DVDs take 80 to 120 ms.

The platters rotate constantly at thousands of RPM; however, to preserve battery, laptops default to powering them down after a set period of no activity. This mechanical action is why hard disks are slowly fading into history and being replaced with SSDs (see SSD). See hard drive capacity, access time and transfer rate.

Disks Come Pre-Formatted
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 emerged. 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 Computer (1956)

Extraordinary technology, IBM's RAMAC was part computer, part tabulator and the first computer with a hard disk. (Image courtesy of IBM.)

Five Megabytes Total

Each of the RAMAC's 50 platters two feet in diameter held a whopping 100,000 characters. Today, the capacity of all 50 would fit on the head of a pin. (Image courtesy of IBM.)

First Personal Computer Hard Disk (1979)

In 1979, Seagate introduced the first hard disk for personal computers with 5MB on two 5.25" platters, the same capacity as all 50 platters in the RAMAC. Today, platters are 3.5" for desktops and 2.5" and 1.8" for laptops. See ST506. (Image courtesy of Seagate Technology, Inc.)

Four Decades After RAMAC (1998)

This 47GB Seagate drive held 100,000 times as much data as the RAMAC. Today, 20 times more storage is available on a flash drive (see USB drive). (Image courtesy of Seagate Technology, Inc.)

World's Smallest (2005)

The size of a postage stamp, the Microdrive was a less-than-one-inch hard disk for mobile devices with up to 8GB of storage (see Microdrive).

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References in periodicals archive ?

It is all there on your laptop hard drive", said my wife, and I nearly choked on my chicken bun 'muska'.

Sleuths in a tizzy over my laptop history

However, Derek Jones, prosecuting, said they seized a tower computer and laptop hard drive containing 147 indecent images.

Paedo walks free despite sick pics

Now Russian analysts have found files on the assassin's laptop hard drive that refer directly to Gulen, as well as 690 references to the Gulen Hizmet (service in Turkish) and to Nur Cemaati, as Gulen is referred to by his supporters.

New evidence links exiled Turkish cleric to Russian envoy's assassin

He said other people had access to the phone, and denied knowing anything about a laptop hard drive found in a shed.

Cleared of all charges; joiner who denied child sex offences is acquitted

Prosecutor William Douglas-Jones said that on a laptop hard drive found at Wilkin's home were 3,704 indecent images of children aged from 12 to 15 classed as being in category C - showing them in indecent poses but without any sexual activity.

Pervert tried to sell tablet loaded with 'vile' pornography

But police will never know how many victims married Bradbury filmed as he destroyed his laptop hard drive. Canadian police alerted the UK's Child Exploitation and Online Protection Centre about him in July 2012 after he bought a film featuring nude boys but CEOP took no action for 16 months.

PERV DOC USED SPY PEN

Expect to pay about $100 for a new laptop hard drive. If you don't already have an external backup drive, get one now.

Repair a buried cable

For example, in the situation discussed above, the company could recover screenshots of the Gmail accessed by the employee from the laptop hard drive, but would be in violation of the SCA if it used the employee's Gmail password (which also is often recoverable from the hard drive) to gain access to the Gmail account on the Internet.

Digital privacy: ready or not, here it comes

Capability: The OWC Do-It-Yourself Hard Drive Kit allows the upgrade of a laptop hard drive to a new faster, larger drive without sending the computer out for repairs.

Techy DYI

Using readily available software, organizations can selectively store data on any media device--a disk system, a backup tape, a laptop hard drive, or even a smart phone--in encrypted or scrambled form that requires a special code or key to make it intelligible.

Encryption--the last line of defense: no security system is perfect, and all measures, no matter how elaborate, are subject to failure

"I'm going to cook dinner,'' he announced, and showed me his collection of recipes, gleaned from the internet and stored on his laptop hard drive. Sometimes I wonder how The Boy would manage without the internet.

The Boy's shaping up to be a domestic god

CMS offers an extensive line of laptop hard drive upgrades, as well as a full suite of data security products for business powered by CE-Secure data encryption software.