Virtual memory is found among all computer operating systems and it provides some very practical benefits to PC users. All computer systems have their own RAM (Physical Random Access Memory) which commonly ranges from 64 to 256 megabytes. When virtual memory is being used, the system allows the users to carry on working without worrying about the availability of data storage or memory saturation. It is often addressed as logical memory and allows users to access a larger volume of memory, allowing them to use more applications simultaneously.
With virtual memory, the system is able to search for applications on the RAM that aren't being used and copies the same on to the hard disk. As a result, more space is freed up on RAM and new applications can be loaded that need to be immediately used. The entire process is done automatically and the user doesn't need to click on anything. It functions by dividing the address space of the application programs into many smaller pages. These smaller pages are 4K byte pages, each with various virtual memory addresses.
Paging is the process by which the dormant (not-in-current use) virtual pages are saved on to the hard disk and are then restored to real memory when the user needs to operate a particular application. Page tables are used by computer operating systems to temporarily save the mapping of this swap between the virtual addresses of various applications and physical addresses (RAM). That part of the hard disk on which the pages are temporarily saved is called a page file.
The ability to save these temporary addresses on the hard disk isn't dependent on the limitations of the RAM alone. There is an automated calculation of the available page file also. Thus, systems that have smaller RAMs would need to have bigger page files. As a result, it is necessary to ensure that size of the page file has been set at its maximum possible value.
Every operating system has its own Paging Supervisor to manage the page tables. Paging Supervisors are very effective in searching for files in the physical memory that are the least used and can be utilized for swapping with virtual memory files. However, there are some pages that cannot be swapped and are called non-pageable or resident pages.
A computer system using virtual memory has access to a more economic way of creating more storage space. Hard-disk space is much cheaper than the RAM chips that are installed in the PC. By using virtual memory, the need to upgrade/add the RAM is avoided.