The memory management subsystem is one of the most important parts of the operating system. Since the •early days of computing, there has been a need for more memory than exists physically in a system. Strategies have been developed to overcome this limitation and the most successful of these is virtual memory. Virtual memory makes the system appear to have more memory than is physically present by sharing it among competing processes as they need it. Virtual memory does more than just make your computer's memory go farther.