Deadlock

Consider the following policies for preventing deadlock in a system with mutually exclusive resources. I. Processes should acquire all their resources at the beginning of execution. If any resource is not available, all resources acquired so far are released II. The resources are numbered uniquely, and processes are allowed to request for resources only in increasing resource numbers III. The resources are numbered uniquely, and processes are allowed to request for resources only in decreasing resource numbers IV. The resources are numbered uniquely. A process is allowed to request only for a resource with resource number larger than its currently held resources Which of the above policies can be used for preventing deadlock?

A system contains three programs and each requires three tape units for its operation. The minimum number of tape units which the system must have such that deadlocks never arise is _____.