The storage devices are those devices  which can be used of storing process. The computer system uses variety of devices for storing the instructions and data which are required for its  operations. Normally we classify the information to be stored on computer in two basic categories Data and the Instructions.

The storage device along with the  algorithm or information on how to control and manage these storage device constitute the memory system of a computer.

These consist of the small set of high speed registers which are internal to a processor and are used as temporary locations where actual processing is done.

It is large memory which is fast but not as fast as internal processor memory. This memory is accessed directly by processor. It is mainly based on integrated circuits.

Secondary memory in fact is much larger in size than main memory but is slower than main memory. It normally stores system programs, other instructions, programs and data files. Secondary can also be used as an overflow memory in case the main memory capacity has been exceeded. 

There is another kind of memory which is increasing being used in modern computers, this is called Cache memory. It is logically positioned between the internal memory and main memory.

RAM is the mode in which and memory location can be accessed in any order in the same amount of time. Ferrite and Semiconductor memories which generally constitute main memory are of this nature. The storage location can be accessed independently and there exit separate access mechanism for each location.