Hard disk facts for kids
A hard disk drive (HDD), hard disk or hard drive, is something used by computers to store information. Hard disks use magnetic recording (similar to the way recording is done on magnetic tapes) to store information on rotating circular platters. The capacity of a hard drive is usually measured in gigabytes (GB), however hard disc capacity can also be measured in terabytes when the capacity is over 1000 gigabytes. A gigabyte is one thousand megabytes and a megabyte is one million bytes, which means that a gigabyte is one billion bytes. Some hard drives are so large that their capacity is measured in terabytes, (TB) where one terabyte is a thousand gigabytes (1 TB = 1000 GB). Very early Consumer Grade hard drives were measured in megabytes.
Different interfaces
Over the years there have been many disk interface types, though all used the same rotating platter recording technology. Differences were in how the data was encoded to binary, data integrity, data transfer speeds, cabling requirements, and cost. As there are different kinds of hard disks, there are also different kinds of interfaces. In 2009, it was common to attach a hard disk using a Serial ATA connection. The connection that came before that was called "IDE" and is called Parallel ATA today. In large data centers, Fibre Channel is often used.
For servers, the SCSI (pronounced 'scuzzy') interface is very popular. There are several types and versions of SCSI interface, like parallel and Serial Attached SCSI, each stepping-up in terms of speed and price. Within servers, several SCSI drives are often used in conjunction with each other, in order to safeguard against data loss or corruption (this is known as RAID - and there are many configurations to choose from).
Related pages
Images for kids
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Internals of a 2.5-inch laptop hard disk drive
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A disassembled and labeled 1997 HDD lying atop a mirror
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Destroyed hard disk, glass platter visible
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Recording of single magnetisations of bits on a 200 MB HDD-platter (recording made visible using CMOS-MagView).
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An HDD with disks and motor hub removed, exposing copper-colored stator coils surrounding a bearing in the center of the spindle motor. The orange stripe along the side of the arm is a thin printed-circuit cable, the spindle bearing is in the center and the actuator is in the upper left.
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Head stack with an actuator coil on the left and read/write heads on the right
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Close-up of a single read-write head, showing the side facing the platter
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Leading-edge hard disk drive areal densities from 1956 through 2009 compared to Moore's law. By 2016, progress had slowed significantly below the extrapolated density trend.
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Two Seagate Barracuda drives, from 2003 and 2009 - respectively 160GB and 1TB. As of 2022[update] Seagate offers capacities up to 20TB.
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8-, 5.25-, 3.5-, 2.5-, 1.8- and 1-inch HDDs, together with a ruler to show the size of platters and read-write heads
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A newer 2.5-inch (63.5 mm) 6,495 MB HDD compared to an older 5.25-inch full-height 110 MB HDD
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Inner view of a 1998 Seagate HDD that used the Parallel ATA interface
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2.5-inch SATA drive on top of 3.5-inch SATA drive, showing close-up of (7-pin) data and (15-pin) power connectors
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Close-up of an HDD head resting on a disk platter; its mirror reflection is visible on the platter surface. Unless the head is on a landing zone, the heads touching the platters while in operation can be catastrophic.
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Two 2.5" external USB hard drives
See also
In Spanish: Unidad de disco duro para niños
