MARKET DESKTOP HDDS

Market segments Desktop HDDs

They typically store between 60 GB and 4 TB and rotate at 5,400 to 10,000 rpm, and have a media transfer rate of 0.5 Gbit/s or higher (1 GB = 109 bytes; 1 Gbit/s = 109 bit/s). As of August 2014, the highest-capacity desktop HDDs store 8 TB.[87][133]

Mobile (laptop) HDDs

Smaller than their desktop and enterprise counterparts, they tend to be slower and have lower capacity. Mobile HDDs spin at 4,200 rpm, 5,200 rpm, 5,400 rpm, or 7,200 rpm, with 5,400 rpm being typical. 7,200 rpm drives tend to be more expensive and have smaller capacities, while 4,200 rpm models usually have very high storage capacities. Because of smaller platter(s), mobile HDDs generally have lower capacity than their greater desktop counterparts.

There are also 2.5-inch drives spinning at 10,000 rpm, which belong to the enterprise segment with no intention to be used in laptops.

Enterprise HDDs

Typically used with multiple-user computers running enterprise software. Examples are: transaction processing databases, internet infrastructure (email, webserver,  e-commerce), scientific computing software, and nearline storage management software. Enterprise drives commonly operate continuously ("24/7") in demanding environments while delivering the highest possible performance without sacrificing reliability. Maximum capacity is not the primary goal, and as a result the drives are often offered in capacities that are relatively low in relation to their cost. [134]

The fastest enterprise HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s [135] and a sustained transfer rate up to 1 Gbit/s. [135] Drives running at 10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have less air drag) and therefore generally have lower capacity than the highest capacity desktop drives. Enterprise HDDs are commonly connected through Serial Attached SCSI (SAS) or Fibre Channel (FC). Some support multiple ports, so they can be connected to a redundant host bus adapter.

Enterprise HDDs can have sector sizes larger than 512 bytes (often 520, 524, 528 or 536 bytes). The additional per-sector space can be used by hardware RAID controllers or applications for storing Data Integrity Field (DIF) or Data Integrity Extensions (DIX) data, resulting in higher reliability and prevention of silent data corruption.[136]

Consumer electronics HDDs

They include drives embedded into digital video recorders and automotive vehicles. The former are configured to provide a guaranteed streaming capacity, even in the face of read and write errors, while the latter are built to resist larger amounts of shock.

Manufacturers and sales

Diagram of HDD manufacturer consolidation

See also: History of hard disk drives and List of defunct hard disk manufacturers

More than 200 companies have manufactured HDDs over time. But consolidations have concentrated production into just three manufacturers today: Western Digital, Seagate, and Toshiba.

Worldwide revenues for disk storage were $32 billion in 2013, down about 3% from 2012.[4] This corresponds to shipments of 552 million units in 2013 compared to 578 million in 2012 and 622 million in 2011.[4] The estimated 2013 market shares are about 40–45% each for Seagate and Western Digital and 13–16% for Toshiba.

External hard disk drives

External HDDs[n] typically connect via USB; variants using USB 2.0 interface generally have slower data transfer rates when compared to internally mounted hard drives connected through SATA. Plug and play drive functionality offers system compatibility and features large storage options and portable design.

External HDDs are usually available as pre-assembled integrated products, but may be also assembled by combining an external enclosure (with USB or other interface) with a separately purchased HDD. They are available in 2.5-inch and 3.5-inch sizes; 2.5-inch variants are typically called portable external drives, while 3.5-inch variants are referred to asdesktop external drives. "Portable" drives are packaged in smaller and lighter enclosures than the "desktop" drives; additionally, "portable" drives use power provided by the USB connection, while "desktop" drives require external power bricks.

As of April 2014, capacities of external HDDs generally range from 160 GB to 6 TB; common sizes are 160 GB, 250 GB, 320 GB, 500 GB, 640 GB, 750 GB, 1 TB, 2 TB, 3 TB, 4 TB, 5 TB and 6 TB.[137][138] Features such as biometric security or multiple interfaces (for example, Firewire ) are available at a higher cost.[139]

There are pre-assembled external hard disk drives that, when taken out from their enclosures, cannot be used internally in a laptop or desktop computer due to embedded USB interface on their printed circuit boards, and lack of SATA (or Parallel ATA) interfaces.[140][141]

Visual representation

Hard disk drives are traditionally symbolized as a stylized stack of platters or as a cylinder, and are as such found in various diagrams; sometimes, they are depicted with small lights to indicate data access. In most modern graphical user environments (GUIs), hard disk drives are represented by an illustration or photograph of the drive enclosure.

                Automatic acoustic management

                Cleanroom

                Click of death

                Data erasure

                Drive mapping

                Hybrid drive

                Microdrive

                RAID

                S.M.A.R.T.

                Solid-state drive

                Write precompensation