Main memory unit is the storage unit, There are several location for storing information in the main memory module.
The capacity of a memory module is specified by the number of memory location and the information stored in each location.
A memory module of capacity 16 X 4 indicates that, there are 16 location in the memory module and in each location, we can store 4 bit of information.
We have to know how to indicate or point to a specific memory location. This is done by address of the memory location.
We need two operation to work with memory.