Define the Global vs. local variables
It is also important to discuss the scope of resources being granted to the application program. Variable scoping is defined as the accessibility of variables by application components.For instance variables may have local or global scope in single-threaded programs. Local variables can only be accessed within the boundaries of the procedure that defines them. Global variables, however, can be seen by the entire application. Variables are accessible over program components for which they are defined.
With the introduction of multithreaded programs, however, the scoping of variables changes. Some programs may want to share access to global information between separately executing processes. Mechanisms must be provided by the operating systems for such accessibility. It may also be necessary to have some data items globally accessible but on a per-thread basis. The following section on per-thread scoping deals with specific thread-level scoping issues.