How-To Geek

Hard Drive (HDD)

The hard drive (or Hard Disk Drive, hence HDD) is the primary storage medium on most computers. Traditionally computer hard drives were (and largely still are) aluminum or glass platters impregnated with a ferro-magnetic material. Data is written, via a simple binary 0/1 system using the polarity of the particles, to the platters using a tiny read/write head attached to a small mechanical arm. Large capacity drives generally have multiple platters.

Hard drive performance is generally quantified with a variety of numbers. These include the rotation speed of the physical platters, noted in Revolutions Per Minute (RPM), which typically ranges from 5,400 to 15,000 RPM, as well as the data access time, noted in milliseconds, and transfer speeds, noted in megabytes per second (e.g. 600 MB/s).

Hard drives with physical platters are slowly being replaced by Solid State Drives (SSDs): storage drives that feature solid state flash memory as a storage medium, instead of magnetic disks.

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