Q. Show the Memory Hierarchy of computer system ?

Memory in a computer system is essential for storage and subsequent retrieval of instructions and data. A computer system uses a variety of devices for storing these instructions and data that are needed for its operation. Usually we classify the information to be stored into two fundamental categories: Data and Instructions. However what is a memory system?

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

A memory system is a very simple system yet it shows a wide range of technology and types. The essential purpose of a computer system is to increase the speed of computation. Similarly the fundamental purpose of a memory system is to provide fast and uninterrupted access by processor to memory such that processor can operate at the speed it is expected to work.

However does this kind of technology where there is no speed gap amid processor and memory speed exist? Answer is yes, it does. Unfortunately as access time (time taken by CPU to access a location in memory) becomes less cost per bit of memory becomes higher. Additionally these memories need power supply until information needs to be stored. Both these things aren't very convenient however on the other hand memories with smaller cost have very high access time which will result is in slower operation of CPU. So cost versus access time anomaly has led to a hierarchy of memories where we supplement fast memories with larger and cheaper as well as slower memories. These memory units can have very different operational and physical characteristics thus memory system is very diverse in cost, type, organisation, technology and performance.  This memory hierarchy will work only if frequency of access to slower memories is considerably less than faster memories. The memory hierarchy system comprises all storage devices employed in a computer system from slow but high capacity auxiliary memory to a relatively faster main memory to an even smaller and faster cache memory accessible to high speed registers and processing logic. Figure below illustrates components of a typical memory system.

Figure: The Memory Hierarchy (Block Diagram)