Hard disk drive
Electro-mechanical magnetic storage device with rotating platters and moving heads.
A hard disk drive (HDD)—also called a hard disk, hard drive, or fixed disk—is an electro-mechanical device for storing digital data. It uses magnetic storage: one or more rigid platters coated with magnetic material spin rapidly, while magnetic heads on a moving actuator arm read and write data to the platter surfaces. Data can be accessed randomly, meaning any block can be retrieved in any order. HDDs are non-volatile, so they retain data when powered off. Modern HDDs typically come as a small rectangular box, sometimes inside a portable enclosure, and unlike the removable-media drives of the 1960s and 1970s, they do not have removable media.
IBM introduced the first disk drive, the 350 for the 305 RAMAC, in 1956. By the early 1960s, disk drives had become the dominant secondary storage for general-purpose computers, a position they held through the eras of servers and personal computers. However, high-volume personal devices like mobile phones and tablets now use flash memory storage. Over 224 companies have manufactured HDDs historically, but after extensive consolidation, most units come from Seagate, Toshiba, and Western Digital. HDDs still dominate the volume of storage produced for servers (measured in exabytes per year). Although production is growing slowly in exabytes shipped, sales revenues and unit shipments are declining because solid-state drives (SSDs) offer higher data-transfer rates, higher areal storage density, somewhat better reliability, and much lower latency and access times.
SSD revenues, mostly from NAND flash memory, slightly surpassed HDD revenues in 2018, and flash storage products now have more than twice the revenue of HDDs. Although SSDs cost four to nine times more per bit, they are replacing HDDs in applications where speed, power consumption, small size, high capacity, and durability matter. As of the source, the cost per bit of SSDs was falling, narrowing the price gap with HDDs.
The main characteristics of an HDD are its capacity and performance. Capacity is given in unit prefixes based on powers of 1000: a 1-terabyte (TB) drive holds 1,000 gigabytes, where 1 gigabyte equals 1,000 megabytes, 1,000,000 kilobytes, or 1,000,000,000 bytes. Some capacity is unavailable to the user because it is used by the file system, operating system, or built-in redundancy for error correction and recovery.
Quick Facts
- Invent-Date
- 1954-12-24This is the original filing date of the application which led to US Patent 3,503,060, generally accepted as the definitive hard disk drive patent.
- Invent-Name
- IBM team led by Rey Johnson
Facts from the source article.
Lore & Background
IBM introduced the first disk drive, the 350 for the 305 RAMAC, in 1956. It was approximately the size of two large refrigerators and stored five million six-bit characters (3.75 megabytes) on a stack of 52 disks. In 1961, IBM announced the 1301 disk storage unit, which used an array of 48 heads and supported cylinder-mode read/write operations. The 1301 cabinet was about the size of three large refrigerators. In 1962, IBM introduced the model 1311, which was about the size of a washing machine and stored two million characters on a removable disk pack. In 1973, IBM introduced a new type of HDD code-named 'Winchester', whose heads were not withdrawn completely from the platters when powered down but instead landed on a special area of the disk surface. In 1974, IBM introduced the swinging arm actuator, which became universal for all HDDs. Over time, recording densities increased and disk diameters reduced to 3.5-inch and 2.5-inch. By 1986, 10 MB was the most commonly used hard disk size, and by the late 1980s, hard drives were standard on all but the cheapest computers.
Reader's Guide
Hard disk drives were the dominant secondary storage device for general-purpose computers beginning in the early 1960s and maintained this position into the modern era of servers and personal computers. More than 224 companies have produced HDDs historically, though after extensive industry consolidation, most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced (exabytes per year) for servers. However, sales revenues and unit shipments are declining because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, somewhat better reliability, and much lower latency and access times. The revenues for SSDs slightly exceeded those for HDDs in 2018, and flash storage products had more than twice the revenue of hard disk drives. Though SSDs have four to nine times higher cost per bit, they are replacing HDDs in applications where speed, power consumption, small size, high capacity and durability are important. The cost per bit of SSDs was falling, and the price premium over HDDs had narrowed. The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000, while most operating systems report capacities in powers of 1024, resulting in a smaller number than advertised. Performance is specified by average access time, average latency (a function of rotational speed), and data rate.
Did You Know?
- The first production IBM hard disk drive, the 350, shipped in 1957 as a component of the IBM 305 RAMAC system.
- The IBM 1301 disk storage unit used an array of 48 heads, one per surface used, and supported cylinder-mode read/write operations.
- In 1973, IBM introduced the 'Winchester' HDD, whose heads landed on a special area of the disk surface when powered down.
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