Hard disk drive

Hard Disk Drive

A hard disk drive (HDD), also known as a hard drive, hard disk, or fixed disk, is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. HDDs are a type of non-volatile storage, retaining stored data even when powered off.

Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. They have maintained this position into the modern era of servers and personal computers. More recently, the emergence of solid-state drives (SSDs) has begun to gradually replace HDDs in some aspects due to SSDs' higher data transfer rates, lower latency, and more reliable performance with no moving parts. However, HDDs remain the preferred choice for bulk storage in data centers and consumer computers due to their cost-per-bit advantage.

History

The history of the hard disk drive is a tale of continuous innovation and refinement. The first HDD, the IBM 350 Disk File, was developed as a part of the IBM 305 RAMAC computer system, offering a storage capacity of 5 million 6-bit characters (about 3.75 megabytes). Over the decades, the storage capacity of HDDs has grown exponentially, from megabytes to several terabytes, thanks to advancements in magnetic recording technologies, including the transition from longitudinal recording to perpendicular recording in the early 21st century.

Technology

HDD technology is based on the principles of magnetic storage. Data is written to the disk by magnetizing a thin film of ferromagnetic material on a disk in a pattern that represents the data. The data is read by detecting the magnetization of the material. A typical HDD design consists of a spindle that holds one or more flat circular disks (called platters), onto which the data is recorded. The platters are made from a non-magnetic material, usually aluminum or glass, and are coated with a thin layer of magnetic material. Read-and-write heads are positioned on an armature or actuator arm that moves over the platter as it spins.

Performance

The performance of an HDD is determined by several factors, including the rotational speed of the platters (measured in revolutions per minute, or RPM), the speed at which the data is transferred to and from the disk (data transfer rate), and the time it takes for the read/write heads to move between tracks on the disk (seek time). Modern HDDs operate at speeds ranging from 5,400 to 15,000 RPM, with the higher RPM drives offering better performance.

Capacity

The storage capacity of HDDs has increased dramatically over time, from the few megabytes in early models to several terabytes in modern drives. This increase has been achieved through improvements in the density of data that can be stored on the disk surface, known as areal density.

Reliability and Failure

HDDs are subject to both operational wear and physical damage. Common failure modes include head crashes, motor failure, and bad sectors. Data recovery from damaged HDDs can sometimes be possible but is often costly and not guaranteed to succeed.

Future

While SSDs are becoming more popular for certain applications, HDDs continue to be used extensively where cost per gigabyte is a critical factor. Innovations such as helium-filled drives and shingled magnetic recording (SMR) have further increased the storage capacity and reduced the cost per bit of HDDs.

See Also

• Solid-state drive
• Data storage device
• Magnetic storage
• Computer storage