Hard disk drive

Partially disassembled IBM 350 (RAMAC)
Internals of a 2.5-inch laptop hard disk drive
A disassembled and labeled 1997 HDD lying atop a mirror
Magnetic cross section & frequency modulation encoded binary data
Destroyed hard disk, glass platter visible
Diagram labeling the major components of a computer HDD
Recording of single magnetisations of bits on a 200 MB HDD-platter (recording made visible using CMOS-MagView).
Longitudinal recording (standard) & perpendicular recording diagram
An HDD with disks and motor hub removed, exposing copper-colored stator coils surrounding a bearing in the center of the spindle motor. The orange stripe along the side of the arm is a thin printed-circuit cable, the spindle bearing is in the center and the actuator is in the upper left.
Head stack with an actuator coil on the left and read/write heads on the right
Close-up of a single read-write head, showing the side facing the platter
Leading-edge hard disk drive areal densities from 1956 through 2009 compared to Moore's law. By 2016, progress had slowed significantly below the extrapolated density trend.
Two Seagate Barracuda drives, from 2003 and 2009 - respectively 160GB and 1TB. Seagate offers capacities up to 20TB.
8-, 5.25-, 3.5-, 2.5-, 1.8- and 1-inch HDDs, together with a ruler to show the size of platters and read-write heads
A newer 2.5-inch (63.5 mm) 6,495 MB HDD compared to an older 5.25-inch full-height 110 MB HDD
Inner view of a 1998 Seagate HDD that used the Parallel ATA interface
2.5-inch SATA drive on top of 3.5-inch SATA drive, showing close-up of (7-pin) data and (15-pin) power connectors
Close-up of an HDD head resting on a disk platter; its mirror reflection is visible on the platter surface. Unless the head is on a landing zone, the heads touching the platters while in operation can be catastrophic.
Two 2.5" external USB hard drives
Diagram of HDD manufacturer consolidation

Electro-mechanical data storage device that stores and retrieves digital data using magnetic storage and one or more rigid rapidly rotating platters coated with magnetic material.

- Hard disk drive

500 related topics


Seagate Technology

American data storage company.

First Seagate logo and wordmark, used from 1986 to 2002
Seagate ST-225, cover removed
Former Seagate Technology headquarters during the 2010s in Cupertino, California
Former Seagate Technology headquarters prior to 2010 in Scotts Valley, California

Seagate developed the first 5.25-inch hard disk drive (HDD), the 5-megabyte ST-506, in 1980.

Western Digital

Western Digital Paradise VGA card, 8-bit ISA bus, circa 1989
Western Digital Tidbit 60 (WDAH260) - 62.3 MB (2.5 inch drive mounted in 3.5 inch adapter bracket)
Western Digital Caviar 80 MB (model number WDAC280-32), from a series of HDDs for desktop PCs; it is a 3.5-inch HDD mounted onto a 5.25-inch adapter bracket.
Western Digital WD740GD 74 GB Raptor, a 10,000 rpm 3.5-inch HDD
Two third-generation 1 TB VelociRaptors in IcePack mounting frames
Western Digital "Red" 4 TB, a NAS-optimized 3.5-inch SATA HDD
A red redesigned My Passport Ultra Drive with a storage of 2TB
WD Elements Portable with 2TB of storage from 2022
WD Elements Portable with 2TB of storage from 2016
First headquarters of Western Digital (then General Digital) in Newport Beach, California, pictured in 1971
WD33C93 single-chip SCSI interface

Western Digital Corporation (WDC, commonly known as Western Digital or WD) is an American computer hard disk drive manufacturer and data storage company, headquartered in San Jose, California.


Japanese multinational conglomerate headquartered in Minato, Tokyo.

AM-only Toshiba vacuum tube radio (1955).
The Toshiba pavilion at Expo '85.
In 1950, Tokyo Shibaura Denki was renamed Toshiba. This logo, known as the “umbrella logo”, was used from 1950–1969, and then as a primary logo between 1969–1984. It was also used later on for hard drives.
Toshiba's secondary logo used from 1969 to 1984, used in tandem with the umbrella logo above.
Toshiba logo, used since 1984.
World-first Japanese word processor Toshiba JW-10 (1979)
Toshiba Science Museum in Kawasaki, Japan
Toshiba factory in Taishi, Japan
The Toshiba research and development facility in Kawasaki, Kanagawa, Japan
Toshiba Europe offices in Neuss, Germany
Toshiba Canada offices
Toshiba television
Toshiba Blu-ray Disc Player
Toshiba HD-DVD Player
Toshiba Qosmio notebook
Toshiba microSD card
Toshiba USB flash drive
Fujitsu Toshiba Regza smartphone
Toshiba Air conditioner
Toshiba SCiB rechargeable battery
Toshiba T9769A integrated circuit
Toshiba hard disk
Toshiba Aquilion Prime CT scanner
Toshiba Vantage Titan MRT-2004 MRI scanner
Toshiba medical ultrasound scanner
ToshibaVision screen in use during the ball drop in Times Square from 2008 to 2018
Toshiba elevator in Taipei 101
Toshiba locomotive Class HD300
Toshiba battery
Toshiba microwave oven
Toshiba rice cooker

Its diversified products and services include power, industrial and social infrastructure systems, elevators and escalators, electronic components, semiconductors, hard disk drives (HDD), printers, batteries, lighting, as well as IT solutions such as quantum cryptography which has been in development at Cambridge Research Laboratory, Toshiba Europe, located in the United Kingdom, now being commercialised.


American multinational technology corporation headquartered in Armonk, New York, with operations in over 171 countries.

NACA researchers using an IBM type 704 electronic data processing machine in 1957
An IBM System/360 in use at the University of Michigan c. 1969
IBM guidance computer hardware for the Saturn V Instrument Unit
IBM inventions: (clockwise from top-left) the hard-disk drive, DRAM, the UPC bar code, and the magnetic stripe card
Pangu Plaza, one of IBM's offices in Beijing, China
Blue Gene was awarded the National Medal of Technology and Innovation in 2009.
IBM Q System One (2019), the first circuit-based commercial quantum computer
The Thomas J. Watson Research Center in Yorktown Heights, New York, is one of 12 IBM research labs worldwide.
IBM Fellow Benoit Mandelbrot discusses fractal geometry, 2010.
IBM ads at John F. Kennedy International Airport, 2013
New IBM employees being welcomed to a bootcamp at IBM Austin, 2015
Employees demonstrating IBM Watson capabilities in a Jeopardy! exhibition match on campus, 2011

Inventions by IBM include the automated teller machine (ATM), the floppy disk, the hard disk drive, the magnetic stripe card, the relational database, the SQL programming language, the UPC barcode, and dynamic random-access memory (DRAM).

Non-volatile memory

Type of computer memory that can retain stored information even after power is removed.

Modern DDR4 SDRAM module, usually found in desktop computers.

Other examples of non-volatile memory include read-only memory (ROM), EPROM (erasable programmable ROM) and EEPROM (electrically erasable programmable ROM), ferroelectric RAM, most types of Computer data storage devices (e.g. disk storage, hard disk drives, optical discs, floppy disks, and magnetic tape), and early computer storage methods such as punched tape and cards.

Solid-state drive

Solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage.

250 GB mSATA SSD with an external enclosure
512 GB Samsung M.2 NVMe SSD
An Intel mSATA SSD
An M.2 (2242) solid-state-drive (SSD) connected into USB 3.0 adapter and connected to computer.
An SSD with 1.2 TB of MLC NAND, using PCI Express as the host interface
An SSD with a 2.5-inch HDD form factor, opened to show solid-state electronics. Empty spaces next to the NAND chips are for additional NAND chips, allowing the same circuit board design to be used on several drive models with different capacities; other drives may instead use a circuit board whose size increases along with drive capacity, leaving the rest of the drive empty
A 2 GB disk-on-a-module with PATA interface
SSD benchmark, showing about 230 MB/s reading speed (blue), 210 MB/s writing speed (red) and about 0.1 ms seek time (green), all independent from the accessed disk location.
CompactFlash card used as an SSD
An SSD that uses NVM Express as the logical device interface, in the form of a PCI Express 3.0 ×4 expansion card
Viking Technology SATA Cube and AMP SATA Bridge multi-layer SSDs
Viking Technology SATADIMM based SSD
MO-297 SATA drive-on-a-module (DOM) SSD form factor
A custom-connector SATA SSD

It is also sometimes called a semiconductor storage device, a solid-state device or a solid-state disk, even though SSDs lack the physical spinning disks and movable read–write heads used in hard disk drives (HDDs) and floppy disks.

Block (data storage)

Sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size.

Computer simulation, one of the main cross-computing methodologies.

Blocking is almost universally employed when storing data to 9-track magnetic tape, NAND flash memory, and rotating media such as floppy disks, hard disks, and optical discs.


Multiple of the unit byte for digital information.

This 2.5 inch hard drive can hold 500 GB (i.e., 500 billion bytes) of data.

This definition is used in all contexts of science (especially data science), engineering, business, and many areas of computing, including storage capacities of hard drives, solid state drives, and tapes, as well as data transmission speeds.

File system

Method and data structure that the operating system uses to control how data is stored and retrieved.

An example of slack space, demonstrated with 4,096-byte NTFS clusters: 100,000 files, each five bytes per file, which equal to 500,000 bytes of actual data but require 409,600,000 bytes of disk space to store
File systems may become fragmented
Directory listing in a Windows command shell

As of 2019, hard disk drives have been key storage devices and are projected to remain so for the foreseeable future.

Serial ATA

SATA 6 Gbit/s host controller, a PCI Express ×1 card with Marvell chipset
SATA 2 connectors on a computer motherboard, all but two with cables plugged in. Note that there is no visible difference, other than the labeling, between SATA 1, SATA 2, and SATA 3 cables and connectors.
2.5-inch SATA drive on top of a 3.5-inch SATA drive, close-up of data and power connectors. Also visible are 8 jumper pins on the 3.5-inch drive.
A fifteen-pin SATA power connector (this particular connector is missing the orange 3.3 V wire)
A 1.8-inch micro SATA hard drive with numbered data and power pins on the connector.
The official eSATA logo
SATA (left) and eSATA (right) connectors
eSATA ports
eSATAp port
Two SATA Express connectors (light gray) on a computer motherboard; to the right of them are common SATA connectors (dark gray)
Size comparison of mSATA (left) and M.2 (size 2242, right) SSDs
An M.2 (2242) solid-state-drive (SSD) connected into USB 3.0 adapter and connected to computer.
SATA topology: host (H), multiplier (M), and device (D)
PATA hard disk with SATA converter attached.
A seven-pin SATA data cable (left-angled version of the connector)
SATA connector on a 3.5-inch hard drive, with data pins on the left and power pins on the right. The two different pin lengths ensure a specific mating order; the longer lengths are ground pins and make contact first.
SATA 3.0 (6 Gbit/s) cable showing the two foil shielded differential pairs.
A six-pin slimline SATA power connector
The back of a SATA-based slimline optical drive

Serial ATA (SATA, abbreviated from Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives.