Secondary / Auxiliary Storage Devices
The auxiliary storage memory is also known as the secondary or external memory. This memory stores a large amount of data including system program, compiler, translator, assembler and other utilities programs. However, the secondary memory is regarded as non-volatile memory which retains its data even when the computer is turned off. Therefore, it is also called permanent memory.
There are a number of secondary storage devices such as Hard Disk, CD-ROM, Magnetic tape, Magnetic drum and flash memories (USB).
A Hard Disk Drive (HDD) or simply hard drive is counted in non-volatile memory storage which stores data on magnetized surface layers. A hard disk is often called a fixed disk because once it is installed, it will not have to be removed from the computer. A hard disk has a large capacity for storing data, normally measured in Gigabytes. The hard disk is a stack of a few thin metal plates, usually coated on both sides with a magnetized material. Data is stored as magnetic spots on tracks that form concentric circles on the surface of disks. In a hard disk unit, several disks are mounted as a pack on a vertical central shaft. The disks are slightly separated from one another to provide space for the movement of Read/Write head assemblies between them. The shaft revolves spinning the disks at a very high speed and then data is accessed.