__________ provides an interface between a process and the operating system to allow user-level processes to request services of the operating system.

Consider a system with four processes and four resources: P1 holds R1 and requests R2 P2 holds R2 and requests R3 P3 holds R3 and requests R4 P4 holds R4 and requests R2 Each resource has exactly one instance. Which statement is correct?

A system has 18 instances of a single resource type, shared among n processes. If each process requires at most 5 instances, what is the maximum value of n for which the system can guarantee that a deadlock will never occur?