Hard disk: устройство и принцип работы на английском для занятий в ДО

Hard disk

A hard disk is part of a unit -- often called a disk drive, hard drive or hard disk drive -- that stores and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces. Today's computers typically come with a hard disk that can contain anywhere from billions to trillions of bytes of storage.

A hard disk is actually a set of stacked disks, like phonograph records. Each disk has data recorded electromagnetically in concentric circles, or tracks, on the disk. A head, similar to a phonograph arm but in a relatively fixed position, writes or reads the information on the tracks. Two heads, one on each side of a disk, read or write the data as the disk spins. Each read or write operation requires that data be located, an operation called a seek. Data already in a disk cache, however, will be located more quickly.

A hard disk/drive unit comes with a set rotation speed varying from 4,200 revolutions per minute to 15,000 rpm. Most laptop and desktop PCs use hard disks that fall between 5,400 rpm and 7,200 rpm, while hard disks at higher rpm can be found in high-end workstations and enterprise servers. Disk access time is measured in milliseconds. Although the physical location of data can be identified with cylinder, track and sector locations, these are actually mapped to a logical block address (LBA) that works with the larger address range on hard disks.

Hard disks remain a popular data storage option for consumers and enterprises, in spite of the growing popularity and rapidly lowering cost of nonvolatile solid-state flash memory in the form of solid-state drives (SSDs). SSDs fit into the same external and internal drive bays as their HDD counterparts. SSDs may be much faster, more durable and draw less power than hard disks, but they are also more expensive. SSDs are considered a better fit for applications that demand high performance, while HDDs are more often used for high-capacity use cases.

History/development

In 1953, IBM engineers created the first hard disk, which was the size of two refrigerators. The company then shipped the first commercial hard disk-based computer, the 5 MB IBM 305 RAMAC (random access method of accounting and control) in 1956. The storage component of the IBM 305 RAMAC was called IBM 350 Disk Storage. RAMAC disks were 2 feet in diameter, and the storage cost worked out to approximately $10,000 per megabyte. It was nevertheless a huge jump forward in computer storage technology, which had mostly been reliant on magnetic tape. The movable read and write heads of RAMAC enabled semirandom access to data for the first time.

IBM continued to lead the development of hard disk technology over the next couple of decades. In 1961, the drive heads of the IBM 1301 Disk Storage Unit floated on a thin layer of air, which kept the heads and platters closer for an increase in storage density. A couple of years later, IBM introduced the first removable hard drive, the 1311. Its first disk pack, the IBM 1316, consisted of six 14-inch platters and 2.6 MB of storage. This was followed by the IBM 2311 (5 MB) and IBM 2314 (29 MB) disk pack HDDs, the latter the first to be standardized, as it worked across multiple editions of the IBM System/360 mainframe computer system.

Memorex introduced the first IBM-compatible hard disk in 1968. In 1970, the first hard drives with error correction appeared, and Western Digital (at the time named General Digital Corporation) was established. In 1973, IBM released the 3340 -- known as the "Winchester" -- the first sealed hard drive with low-mass heads and lubricated spindles. The first patent for redundant array of independent disks (RAID) technology was filed in 1978, and in 1979, a group headed by Al Shugart, who helped develop RAMAC decades earlier, founded Seagate Technology Corp. That was also the year IBM rolled out its Piccolo drive, which used eight disks to store 64 MB, and the IBM 3370, the first HDD with a thin-film head.

In 1980, IBM released the first gigabyte hard drive, which weighed 550 pounds and was the size of a refrigerator, for $40,000. This was the same year Seagate introduced the first 5.25-inch hard disk. Scottish company Rodime produced a 3.5-inch hard drive in 1983. Three years later, the Small Computer System Interface (SCSI) standard came along. In 1988, PrairieTek shrank the hard drive to 2.5 inches -- 20 MB on two disk platters -- for use in laptops.

With the dawn of the 1990s came IBM's 0663 Corsair drive. Storing up to 1 GB of data on 8.95 mm disks, the 0663 was the first hard disk to use magnetoresistive heads. Drives continued to shrink, with the first 1.8-inch disk coming from Integra Peripherals in 1991 followed by the 1.3-inch Hewlett Packard Kittyhawk in 1992. Western Digital developed the Enhanced IDE hard drive interface, breaking the 528 MB throughput barrier, in 1994. By 1996, IBM was storing 1 billion bits per square inch on a platter, and Seagate's Cheetah family became the first 10,000 rpm HDDs. In 1997, IBM rolled out the 3.5-inch 16.8 GB Titan, the first hard disk to use giant magnetoresistive heads. The company's Microdrive, released the next year, stored 340 MB on a single 1-inch disk platter.

In 2000, Maxtor bought competitor Quantum's hard drive business, and Seagate hit 15,000 rpm with its Cheetah X15 HDD. Seagate achieved another milestone by demonstrating a perpendicular magnetic recording areal density of 100 Gb per square inch that same year. Hitachi bought IBM's data storage business in 2003, Seagate produced the first Serial Advanced Technology Attachment computer bus interface and Western Digital made the first 10,000 rpm SATA hard drive, the 37 GB Raptor. In 2004, Toshiba released the first 0.85-inch hard drive, a 2 GB model on a single platter, while Hitachi shipped the first 500 GB HDD in 2005. In 2006, Seagate acquired Maxtor, further consolidating the hard drive market. Drive capacities continued to skyrocket from there.

Capacity

By the end of the 2000s, Seagate and Western Digital had released the first 3 TB HDDs, with those companies and Toshiba producing the first 4 TB drives early the next decade. In 2013, Seagate had a 5 TB HDD, while HGST (a Western Digital subsidiary) shipped a 6 TB helium-filled hard disk.

Helium offers less drag and turbulence than air because it is less dense and lighter than air. That means drives filled with helium run cooler and faster and can have higher storage densities. In addition, a helium-filled hard disk enables manufacturers to put seven platters in the same space required for five platters in conventional hard drives.

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Also in 2013, Seagate introduced hard disks using shingled magnetic recording (SMR) technology to further overcome the physical limitations of conventional drives. SMR layers magnetic tracks on each disk instead of placing them parallel to each other as in conventional hard disks, thereby increasing storage density. The tracks overlap like shingles on a roof, hence the name of the technology.

Today, thanks in part to the development of helium-based HDDs and SMR technology, hard disk capacities have grown to 10 TB, 12 TB, 14 TB and 16 TB.

Адрес публикации: https://www.prodlenka.org/metodicheskie-razrabotki/325354-hard-disk