Computer possesses memories as human beings. There are two types of computer memory viz., volatile memory and non-volatile memory. As the name recommend volatile memories are not permanent and they go away when there is no power supply to computers. They are also termed as Random Access Memory (RAM). Non-volatile memories do not go away when the computer is switched off. Such types of memories are also called as Read Only Memory (ROM). While we store information in some kind of circuit or device, we not only require some way to store and retrieve it, but also to situate precisely where in the device that it is. Most, if not all, memory devices may be thought of as a series of mailboxes, folders in a file cabinet, or some other metaphor where information may be situated in a variety of places. While we refer to the actual information being stored in the memory device, usually we refer to it as the data.
The position of this data within the storage device is usually called the address, in a manner reminiscent of the postal service. With some kinds of memory devices, the address in which certain data is stored may be called up by means of parallel data lines in a digital circuit. With other types of devices, data is addressed in terms of definite physical location on the surface of some type of media (the tracks and sectors of circular computer disks, for example). However, some memory devices such like magnetic tapes have a one- dimensional type of data addressing: if you desire to play your favourite song in the middle of a cassette tape album, you ought to fast-forward to that spot in the tape, arriving at the appropriate spot by means of trial-and-error, judging the approximate area using a counter that keeps track of tape location, and/or by the amount of time it takes to get there from the starting of the tape.