The paging file is very closely related to the physical RAM installed in the computer.
Its purpose is to extend the amount of physical RAM and make it available to the system. Both services and installed applications can benefit from this ‘extra’ RAM, even though it is substantially different from the sticks that plug into the motherboard. When the load imposed by applications and services running on the computer nears the amount of installed RAM it calls out for more. Since there isn’t any additional RAM to be found, it looks for a substitute; in this case virtual memory which is also known as the page file.
If you are wondering how big your computer’s pagefile is, try running this script to find out.