describe the life circle of process and why each process must have one PCB.

Process is a dynamic entity, from creation to extinction, is the whole life cycle of a process. Processes may experience different states, generally speaking, there are three states:Ready state,Execution status and Blocking state.In the whole life cycle of a process, the system always controls the process through its PCB. The system perceives the existence of the process according to the PCB of the process, not anything else. So, PCB is the only sign of the existence of the process