In computing, environment variables are dynamic named values that affect the way running processes will behave and are part of the environment in which a process runs. Environment variables are used to pass configuration information to processes without the need to modify the code of the programs themselves.
In Windows XP, as in other Windows operating systems, environment variables can be used to store a variety of information, such as the path to the system directory, the location of user-specific files, and the current user’s name. Environment variables can be set and modified using the Control Panel or through the command prompt.