Western Digital Corporation (commonly referred to as Western Digital and often abbreviated as WDC or WD) is an American computer data storage company and one of the largest computer hard disk drive manufacturers in the world, along with its main competitor Seagate Technology.

Western Digital Corporation has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970, by Alvin B. Phillips, a Motorola employee, as General Digital, initially (and briefly) a manufacturer of MOS test equipment. It rapidly became a speciality semiconductor maker, with start-up capital provided by several individual investors and industrial giant Emerson Electric. Around July 1971, it adopted its current name and soon introduced its first product, the WD1402A UART.

Initially financed with start-up capital provided by investors and Emerson Electric Company, WDC made its money by selling calculator chips through the early years of the 1970s, and by 1975 WDC was the largest independent calculator chip maker in the world. The oil crisis of the mid-1970s and the bankruptcy of its biggest calculator customer, Bowmar Instrument, changed its fortunes, however, and in 1976 Western Digital declared Chapter 11 bankruptcy. After this, Emerson withdrew their support of the company, and WDC was on its own.

WDC introduced several landmark products during this time, including the MCP-1600 multi-chip, microcoded CPU. The MCP-1600 was used to implement DEC's LSI-11 system and their own Pascal MicroEngine microcomputer which ran the UCSD p-System Version III and UCSD Pascal. The processor was also used in several single-chip floppy disk drive controller chips, notably the FD1771. However, the WD integrated circuit that arguably drove Western's forward integration was the 1771 chip, the first disk drive formatter/controller, replacing boards of TTL logic. Despite a price far higher than average CMOS chips of the time, it was very successful and extremely profitable.

The FD1771 and its kin were WDC's first entry into the data storage industry; by the early 1980s, they were making hard disk drive controllers, and in 1983, they won the contract to provide IBM with controllers for the PC/AT. That controller, the WD1003, became the basis of the ATA interface (which WDC developed along with Compaq and Control Data Corporation's MPI division, now owned by Seagate Technology), starting in 1986. Throughout most of the 1980s, the family of controllers based on the WD1003 provided the bulk of WDC's revenues and profits, and for a time generated enormous corporate growth.

Much of the mid-to-late 1980s saw an effort by WDC to use the profits from their ATA storage controllers to become a general-purpose OEM hardware supplier for the PC industry. As a result, WDC purchased a number of hardware companies. These included graphics cards (through its Paradise subsidiary, purchased 1986, which became Western Digital Imaging), core logic chipsets (by purchasing Faraday Electronics Inc. in 1987), SCSI controller chips for disk and tape devices (by purchasing ADSI in 1986), networking (WD8003, WD8013 Ethernet and WD8003S StarLAN). They did well (especially Paradise, which produced one of the best VGA cards of the era), but storage-related chips and disk controllers were their biggest money makers. In 1986, they introduced the WD33C93 single-chip SCSI interface, which was used in the first 16-bit bus mastering SCSI host adapter, the WD7000 "FASST"; in 1987 they introduced the WD37C65, a single-chip implementation of the PC/AT's floppy disk controller circuitry, and the grandfather of modern super I/O chips; in 1988 they introduced the WD42C22 "Vanilla", the first single-chip ATA hard disk controller.

1988 also brought what would be the biggest change in WDC's history. That year, WDC bought the hard drive production assets of PC hardware maker Tandon; the first products of that union under WDC's own name were the "Centaur" series of ATA and XT attachment drives.

By 1991, things were starting to slow down, as the PC industry moved from ST-506 and ESDI drives to ATA and SCSI, and thus were buying fewer hard disk controller boards. That year saw the rise of WDC's Caviar drives, brand new designs that used the latest in embedded servo and computerized diagnostic systems.

Eventually, the successful sales of the Caviar drives resulted in WDC starting to sell some of its divisions. Paradise was sold to Philips, and since disappeared. Its networking and floppy drive controller divisions went to SMC Networks and its SCSI chip business went to Future Domain, which was later bought out by market leader Adaptec. Around 1995, the technological lead that the Caviar drives had enjoyed was eclipsed by newer offerings from other companies, especially Quantum Corp., and WDC fell into a slump.

Products and ideas of this time did not go far. The Portfolio drive (a 3-inch (76 mm) form factor model, developed with JT Storage) was a flop, as was the SDX hard disk to CD-ROM interface. WDC's drives started to slip further behind competing products, and quality began to suffer; system builders and PC enthusiasts who used to recommend WD above all else, were going to the competition, particularly Maxtor, whose products had improved significantly by the late 1990s.

In an attempt to turn the tide in 1998, WDC recruited the help of IBM. This agreement gave WDC the rights to use certain IBM technologies, including giant magneto-resistive (GMR) heads and access to IBM production facilities. The result was the Expert line of drives, introduced in early 1999. The idea worked, and WDC regained respect in the press and among users, even despite a recall in 2000 (which was due to bad motor driver chips). WDC later broke ties to IBM.

In 2001, Western Digital became the first manufacturer to offer mainstream ATA hard disk drives with 8 MiB of disk buffer. At that time, most desktop hard disk drives had 2 MB of buffer. WDC labeled these 8 MB models as "Special Edition" and distinguished them with the JB code (the 2 MB models had the BB code). The first 8 MB cache drive was the 100 GB WD1000JB, followed by other models starting with 40 GB capacity. WDC advertised the JB models for cost-effective file servers. In October 2001, WD restated its prior year results to reflect the adoption of SEC Staff Accounting Bulletin No.101 and the reclassification of Connex and SANavigator results as discontinued operations.

In 2003, WD acquired most of the assets of bankrupt one-time market leading magnetic hard drive read-write head developer Read-Rite Corporation. In the same year, WD offered the first 10,000 rpm Serial ATA HDD, the WD360GD "Raptor", with a capacity of 36 GB and an average access time of less than six milliseconds. Soon, the 74 GB WD740GD followed, which was also much quieter. In 2004, Western Digital redesigned its logo for the first time since 1997, with the design of new logo focusing on the company's initials ("WD"). In 2005, Western Digital released the 150 GB version, the WD1500, which was also available in a special version with a transparent window enabling the user to see the drive's heads move over the platters while the drive read and wrote data. As of 2004, the WD Raptor drives have a five-year warranty, making them a more attractive choice for inexpensive storage servers, where a large number of drives in constant use increases the likelihood of a drive failure.

In 2006, Western Digital introduced its My Book line of mass market external hard drives that feature a compact book-like design. On October 7, 2007, Western Digital released several editions of a single 1 TB hard drive, the largest in its My Book line.

In 2007, Western Digital acquired magnetic media maker Komag. Also in the same year, Western Digital adopted perpendicular recording technology in its line of notebook and desktop drives. This allowed it to produce notebook and desktop drives in the largest classes of the time. Western Digital also started to produce the energy efficient GP (Green Power) range of drives notable for their very low power consumption and heat dissipation but surprisingly good performance.

In 2007, Western Digital announced the WD GP drive touting rotational speed "between 7200 and 5400 rpm", which, if potentially misleading, is technically correct; the drive spins at 5405 rpm, and the Green Power spin speed is not variable. WD GP drives are programmed to unload the heads whenever idle for a very short period of time. Many Linux installations write to the file system a few times a minute in the background. As a result, there may be 100 or more load cycles per hour, and the 300,000 load cycles rating of a WD GP drive may be exceeded in less than a year.

On April 21, 2008, Western Digital announced the next generation of its 10,000 rpm SATA WD Raptor series of hard drives. The new drives, called WD VelociRaptor, featured 300 GB capacity and 2.5-inch (64 mm) platters enclosed in the IcePack, a 3.5-inch (89 mm) mounting frame with a built-in heat sink. Western Digital said that the new drives are 35 percent faster than the previous generation. On September 12, 2008, Western Digital shipped a 500 GB 2.5-inch (64 mm) notebook hard drive which is part of their Scorpio Blue series of notebook hard drives.

On January 27, 2009, Western Digital shipped the first 2 TB internal hard disk drive. On March 30, 2009, WDC entered the solid-state drive market with the acquisition of Siliconsystems, Inc. On July 27, 2009, Western Digital announced the first 1 TB mobile hard disk drive, which shipped as both a Passport series portable USB drive as well as a Scorpio Blue series notebook drive.

In April 2010, Western Digital acquired the magnetic glass media sputtering operations of HOYA Corporation and HOYA Magnetics Singapore Pte. Ltd (HOMS). While Western Digital had previously acquired other magnetic glass media sputtering operations, the purchase of HOMS gave Western Digital an edge in its striving to produce high-end hard disk drives using magnetic glass media. By 2010, there were three surviving independent HDD glass media manufacturing plants, namely Showa Denko, Fuji Electric and HOYA Magnetics.

In October 2010, Western Digital announced the first 3 TB internal hard disk drive.

In March 2011, Western Digital agreed to acquire the storage unit of Hitachi, Hitachi Global Storage Technologies, for about $4.3 billion of which $3.5 billion was paid in cash and the rest with 25 million shares of Western Digital. On October 21, 2011, Western Digital's Thailand plant suspended operation in relation to the 2011 Thailand floods. This caused a shortage of hard drives supplied by Western Digital. PC manufacturers noted of the issue with Apple CEO, Tim Cook stating that he was expecting an "overall industry shortage of disk drives." A Dell spokesperson also stated they were "working with our hard drive suppliers to address potential impact for the remainder of the year." Despite this, Western Digital's profits increased following the increase of HDD prices.

In March 2012, Western Digital completed the acquisition of Hitachi Global Storage Technologies and became the largest traditional hard drive manufacturer in the world. To address the requirements of regulatory agencies, in May 2012 WDC divested assets to manufacture and sell 3.5-inch hard drives for the desktop and consumer electronics markets to Toshiba. In July 2012, Western Digital announced a "Red" series of drives, designed for network-attached storage (NAS) devices. This series of drives has a special firmware designed for Home/Small Business environments, has better reliability than standard desktop drives, is more energy efficient and comes with a 3-year warranty. In November 2012, Western Digital announced a 4 TB internal hard disk drive, a 3.5-inch, 7200 rpm drive belonging to the "Black" series.

On January 27, 2013, Timothy Martin Leyden announced WD would invest US $200 million to expand in Thailand. Operations resumed in Thailand after it recovered from damage during the 2011 floods. In November 2013, Western Digital (through its HGST subsidiary) showed off new helium-filled 6 TB Ultrastar He6 hard disk drives. When compared to regular air-filled HDDs, they claim 49% of reduction in power usage per terabyte of storage.

In February 2014, Western Digital announced a new "Purple" line of hard disk drives for use in video surveillance systems, with capacities from 1 to 4 TB. They feature internal optimizations for applications that involve near-constant disk writing, and "AllFrame" technology which is designed to reduce write errors. This line was later expanded to include 5 and 6 TB models. In September 2014, Western Digital's HGST division introduced new helium-filled 6 TB, 8 TB and 10 TB HDDs, out of which the 10 TB variant also utilizes shingled magnetic recording (SMR). In December 2014, Western Digital acquired Skyera, a flash-based storage development company, integrating the newly acquired company into its HGST division.

In May 2015, Western Digital redesigned the My Passport Ultra series of portable hard disk drives, adding a 3 TB storage option. Later in 2015, WDC also launched the WD Blue series of solid-state hybrid drives, with a 4 TB desktop drive (WD40E31X) and a 1 TB laptop drive (WD10J31X) as the first in the series. In August 2015, WDC added higher-capacity (2–6 TB) 5400 rpm models to its Blue hard disk drives series, as well as 5 TB and 6 TB models to its Black and Red Pro hard disk drive series.

In May 2016, Western Digital acquired SanDisk for US$19 billion.

In April 2017 Western Digital moves its headquarters from Irvine, California to San Jose, California.

Western Digital hard drives feature product names based on colors; these colors signify the characteristics of the drive:

Western Digital (WD) distributes the following utilities for use with its hard drives.

Data Lifeguard Tools is a software utility suite for basic setup of hard disks, developed under contract by Kroll Ontrack Inc (who also provides similar suites for other drive manufacturers). It runs on Microsoft Windows and DOS operating systems. It is free to download and use, however doesn't support modern WD drives – an installed drive will be ignored. As of September 30, 2009, Acronis WD Edition replaced Data Lifeguard Tools.

As of version 11 it contains the following features:

Data Lifeguard Diagnostics is a software utility used primarily for determining the physical condition - but only of older models of Western Digital hard drive. It includes features such as:

Western Digital also ships WD Smartware with many of its drives for use as backup drives, with an exception for its Touro Mobile hard drives, which is a HDD brand from its HGST division. Additionally, this software does not detect any HGST-produced hard drives, in contrast with the automatic detection of Western Digital's My Passport or My Passport Ultra hard drives once the user plugs it in a computer where WD Smartware is installed. This software backs up all Documents, Pictures, Movies, Emails, and more on the drive, and continually checks for changes to drive locations. This means that regular backup takes place. The software appears to detect particular hard drives' brand and differs Western Digital hard drives from another hard drives, a similar way to Seagate's SeaTools software.

However, as of June 2013, one can no longer use a boot disc to test a modern WD drive independently of an operating system. In the explanatory note on its support site, Western Digital omits to elaborate on why it forces users to use Windows to test its drives, alluding to an OS X issue: "Due to limitations in Mac OS X, you will need to connect your drive to a PC running Windows in order to run our diagnostics."

WD was the last manufacturer of parallel ATA hard disk drives for laptops (2.5-inch form factor) and desktop PCs (3.5-inch form factor), by producing them until December 2013.

Western Digital sells consumer storage products under the WD brand, with product families called My Passport, My Book and My Cloud.

Western Digital announced products in the over the top set top box market to compete with the Apple TV, Roku, and Google TV.

Western Digital also manufactures networking products. For their wireless router: My Net 600, My Net 750, My Net 900, and My Net 900 Central. For the remaining: My Net AC Bridge, My Net Switch, and My Net Wi-Fi Range Extender.

Lawsuits have been filed against various manufacturers including Western Digital, related to the claimed capacity of their drives. The drives are labelled using the convention of 10^3 (1000) bytes to the kilobyte, resulting in a perceived capacity shortfall when reported by most operating systems, which tend to use 2^10 (1024) bytes to the kilobyte.

While Western Digital maintained that they used "the indisputably correct industry standard for measuring and describing storage capacity", and that they "cannot be expected to reform the software industry", they agreed to settle in March 2006, with a $30 refund to affected customers in the form of backup and recovery software of the same value. A disclaimer is now included with all drives explaining the capacity figures.

Self-encrypting Western Digital hard drives have been reported to have severe faults and to be easy to decrypt.