Whenever you run a program, the RAM area in your PC is loaded with the data needed to run the program. It then resumes loading your program. These libraries can contain many functions that a program must use. Unfortunately, if a program you are running needs only a few of those functions, the program will still use up your RAM as if required for all the functions. However, as your PC's physical memory is obviously much too small to contain the entire contents of your hard disk.
Windows therefore decides which files to store.
It retains in RAM the files that have recently been used and which it thinks are likely to be used again. Yet again, this process uses up RAM and some of the files it stores might not be required again until the next day. The larger and more complex a program is, the more likely it is to contain errors. Many of these are not a major problem and thus go undetected. Starting and Closing Programs When you run a program it loads data into memory.