Data storage devices can be divided into 2 main categories:

Backing storage is used to store programs and data when they are not being used or when a computer is switched off. When programs and data are needed they are copied into main memory but also still remain on backing storage. Magnetic tape drives, floppy disk drives and hard disk drives are all examples of backing storage devices.

The Main Memory contains two types of memory chip called ROM and RAM which hold program instructions and data.