Memory Hierarchy

The total memory capacity of a computer can be visualized by hierarchy of components. This memory hierarchy system consist of all storage devices contained in a computer system from the slow auxiliary memory to fast Main Memory and to smaller Cache memory.
Auxiliary memory access time is generally 1000 times that of the main memory, hence it is the bottom of the hierarchy.
The main memory occupies the central positions because it is equipped to communicate directly with the CPU and with auxiliary memory devices through input/output processor(I/O).
when the program not residing in main memory is needed by the CPU, they are brought in from auxiliary memory. Programs not currently needed in main memory are to provide space in main memory for the other program that are currently use.
The cache memory is used to store program data which is currently being executed in the CPU. Approximate access time ratio between cache memory and main memory is about 1 to 7~10.