The mtoken is common to all interfaces and calls. It is a fullword field provided by the application but with a value set by the fast data access service. An application can have multiple concurrent instances of interaction with fast data. Each instance deals with a single program being inspected, and each has a unique mtoken. The first time the application calls for a particular program it must set the mtoken to 0. The value returned must be used for all subsequent calls up through the call in which the application indicates it is terminating the instance.