What is the difference between user variables and system variables?
Right-click My Computer and go to Properties->Advanced->Environmental Variables…
What’s above are user variables, and below are system variables. The elements are combined when creating the environment for an application. System variables are shared for all users, but user variables are only for your account/profile.
Environment variables are ‘evaluated’ (ie. they are attributed) in the following order:
Variables defined in autoexec.bat
Every process has an environment block that contains a set of environment variables and their values. There are two types of environment variables: user environment variables (set for each user) and system environment variables (set for everyone). A child process inherits the environment variables of its parent process by default.
Programs started by the command processor inherit the command processor’s environment variables.
Environment variables specify search paths for files, directories for temporary files, application-specific options, and other similar information. The system maintains an environment block for each user and one for the computer. The system environment block represents environment variables for all users of the particular computer. A user’s environment block represents the environment variables the system maintains for that particular user, including the set of system environment variables.
GOOD READ: http://stackoverflow.com/