This concept leads us to an important consequence – It is possible for a process to be larger than the size of main memory. So, while developing a new process, it is not required to look for the main memory available in the machine. Because, the process will be divided into pages and pages will be brought to memory on demand.
Because a process executes only in main memory, so the main memory is referred to as real memory or physical memory.

A programmer or user perceives a much larger memory that is allocated on the disk. This memory is referred to as virtual memory. The program enjoys a huge virtual memory space to develop his or her program or software.

The execution of a program is the job of operating system and the underlying hardware. To improve the performance some special hardware is added to the system. This hardware unit is known as Memory Management Unit (MMU).

In paging system, we make a page table for the process. Page table helps us to find the physical address from virtual address.

The virtual address space is used to develop a process. The special hardware unit , called Memory Management Unit (MMU) translates virtual address to physical address. When the desired data is in the main memory, the CPU can work with these data. If the data are not in the main memory, the MMU causes the operating system to bring into the memory from the disk.

A typical virtual memory organization is shown in the Figure 3.24.