Hard disks are storage devices which are permanently connected to the computer system. Hard disks can store programs, data, operating system, compilers, assemblers, application programs, database etc. A metal or metal alloy is preferred as the construction material for a hard disk. Aluminium is a good choice for this. A thin coating of a magnetic material preferably iron oxide is coated over it. Size of hard disk in a laptop is less (almost by one inch) compared to the hard disk of a desktop. Hard disk drive unit is composed of hard disk, read/write heads, access mechanism and a driving motor.
