hard disk drive (HDD)

Contributor(s): Sarah Wilson

A computer hard disk drive (HDD) is the mechanism that controls the positioning, reading and writing of the hard disk, which furnishes data storage. A hard disk drive -- often shortened to hard drive -- and hard disk are not the same thing, but they are packaged as a unit and either term can refer to the whole unit. Hard disk drives can be found in desktop computers, mobile devices, consumer electronics and enterprise storage arrays in data centers.

Bill Hammack, with the
University of Illinois-Urbana's
Department of Chemical & Biomolecular
Engineering, shows how an HDD works.

History of hard disk drives

The hard disk was created in 1953 by engineers at IBM who wanted to find a way to provide random access to high capacities of data at a low cost. The disk drives developed were the size of refrigerators, could store 3.75 megabytes of data and began shipping in 1956. Memorex, Seagate and Western Digital were other early vendors of hard disk drive technology.

Hard disk drive form-factor size has continued to decrease as the technology evolves. By the mid-1980s, 3.5-inch and 2.5-inch form factors were introduced, and it was at this time they first became a standard in personal computers (PCs).

Hard disk drive density has increased since the technology was first developed. The first hard disk drives were able to store megabytes of data, while today they are in the terabyte (TB) range. Hitachi released the first 1 TB hard drives in 2007. In 2015, HGST announced the first 10 TB hard drive.

Hard disk drive components

Most basic hard drives consist of a number of disk platters that are positioned around a spindle inside a sealed chamber. The chamber also includes read-and-write heads and motors.

Hard disk drive components
Hard disk drive components

The motor is used to spin the platters, which hold the data, at up to 15,000 rotations per minute (a higher rpm number results in faster performance). As the platters spin, a second motor controls the position of the read-and-write heads that record information to, and read information from, tracks on each platter.


The main alternative to hard disk drives in PCs and the enterprise are solid-state drives (SSDs).

Discover the differences between a
solid-state drive and hard disk drive
in this video from StaplesTechTV.

Unlike hard disks, SSDs contain no moving parts. SSDs also have a lower latency than HDDs, and are therefore often favored to store critical data that needs to be accessed quickly and for applications with a high input/output demand. However, SSDs are more expensive than HDDs from a price-per-gigabyte standpoint. Many enterprise storage arrays ship with a mix of HDDs and SSDs to reduce costs while providing better performance.

HDD technology developments

In 2013, Seagate announced hard disk drives that use shingled magnetic recording (SMR) technology. SMR increases storage density in hard disk drives by layering the magnetic tracks on each disk, rather than placing them parallel to each other. It is referred to as shingled because the tracks overlap similar to shingles on a roof.

This video from HddSurgery shows
the inside of an HGST helium HDD.

HGST announced the first helium-filled hard disk drive in 2012. Helium is less dense, cooler and lighter than air, and can therefore consume less power, increase drive density and improve performance compared with traditional hard disk drives. In 2016, Seagate announced its own 10 TB helium hard drive.

This was last updated in May 2016

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