Hard disk drives (HDDs) are common storage devices that save data on small magnetic regions of spinning plates.  Since the storage medium is magnetic, the data maintains integrity even without a power source, also known as non-volatile memory.  This storage method has a long history of market domination and has been a critical element in computing since its widespread development in the 1960s. 

The fundamental components of an HDD are the spinning disks (or platters) coated with a ferromagnetic film, the control arm and read/write heads.  In most consumer devices today the disks rotate at a constant 5400 or 7200 RPM.  The read/write heads are slowly arced across the platters when writing or reading, creating or detecting magnetic transitions that are translated into binary information.

 HDDs are susceptible to mechanical wear due to the moving components, as well as thermal interference in the magnetic storage film.  They also have a slow startup and access times due to the mechanical limitations of the device and can easily be damaged if mishandled.  Because of these limitations solid state drives (SSDs) are becoming more competitive in the memory market.