A Hard disc is a secondary data storage device used in computers. It is a very high speed permanent magnetic memory storage device in the form of several platters (plates) with both sides of each platter usable. The ensemble of all platters has one read-write head on each surface.
The platters (disc) rotate at uniform speed when it is on. The read-write head uses electric pulses with synchronized timing at high frequency to write or read data bytes. The data on hard disk is organized in sectors.
A hard disk consumes quite less energy, makes very less noise, low access time, read & write times, and has a long life. Also a hard disk is a fixed and non-removable storage device. Its capacities are in terms of 50 GB to 1 TB.