Hard Disk

A hard disk ,commonly known as a HDD (hard disk drive) or hard drive and formerly known as a fixed disk, is a digitally encoded non-volatile storage device which stores data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to an entire unit containing multiple platters, a read/write head assembly, driver electronics, and motor while "hard disk" (sometimes "platter") refers to the storage medium itself.

Hard disks were originally developed for use only with computers. Though in the 21st century, applications for hard disks have expanded beyond computers to include digital video recorders, digital audio players, personal digital assistants and digital cameras. In 2005 the first mobile phones to include hard disks were introduced by Samsung Group and Nokia. The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as RAID, hardware such as network attached storage (NAS) devices, and systems such as storage area networks (SANs) for efficient access to large volumes of data.