Main memory is also called random access memory (RAM). CPU can access Main memory directly. Data access from main memory is much faster than Secondary memory. It is implemented in a semiconductor technology, called dynamic random-access memory (DRAM).
Main memory is usually too small to store all needed programs. It is a volatile storage device that loses its contents when power is turned off. Secondary memory can stores large amount of data and programs permanently. Magnetic disk is the most common secondary storage device. If a user wants to execute any program it should come from secondary memory to main memory because CPU can access main memory directly.
