Memory locking is a way to ensure that a process stays in main memory and is exempt from paging. In a realtime environment, a system must be able to guarantee that it will lock a process in memory to reduce latency for data access, instruction fetches, buffer passing between processes, and so forth. Locking a process's address space in memory helps ensure that the application's response time satisfies realtime requirements. As a general rule, time-critical processes should be locked into memory. This paper describes the items about “Memory Locking and Unlocking Functions”and“Memory Locking in multiprocesses environment”in a realtime environment.