Memory Hierarchy

Computer memory is any physical device capable of storing information temporarily or permanently. And hierarchy means a system in which members of an organization or society are ranked according to relative status or authority is called hierarchy.

So we can say that “In computer architecture the memory hierarchy is a concept used to discuss performance issues in computer architectural design, The memory hierarchy in computer storage separates each of its levels based on response time.”

Register: - A processor register (CPU register) is one of a small set of data holding places that are part of the computer processor. ... For example, an instruction may specify that the contents of two defined registers be added together and then placed in a specified register.

Cache memory:--Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. 

Primary Memory- Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory.

Secondary Memory:-This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories; instead they are accessed via input-output routines.