If this does not include all of the process' working set , the system may thrash . The contents of ROM are usually set in the factory. In tracing garbage collection , a root holds a reference or set of references to objects that are a priori reachable . The root set is used as the starting point in determining all reachable data. Roots basically comprise the references in the state of the mutator .
Typical roots are global variables, other static data, and the control stack .