The OS controls t tape drives. The Banker's Algorithm says to allocate tape drives to users only when allocaitons result in safe states rather than in unsafe states. Still possible for all three users to finish, i.e., there is at least one way for all users to finish. No matter which user gets the available tape drive none can be guaranteed to finish. An unsafe state implies that some sequence of events might lead to deadlock.
Processes claim exclusive use of the resources they require.
System may either grant or deny each user request. The system grants requests that result in safe states only. Weaknesses requires fixed number of resources to allocate. May not be realistic with breakdowns, repairs, etc. requires fixed number of users. Very difficult in dynamic systems.