The life circle of process



The life circle of process can be defined by a diagram of its different states, which describe different action and situation when a process is in its execution time. As the picture shows, the life circle of process consists of five parts, which is new, ready, waiting, running and terminate. These five different states define the different status of the process. New means the process is being created. Running means the proess are being executed. Waiting means the process is waiting for some event to occur. Terminated means the process has finished execution.

During the life circle or the life time of a process, it begins with the new state, end with the terminate state and can changes among ready, running and waiting status, according to the different operations of the computer.

 

Why each process must have one PCB

PCB, the process control blcok is used to represent each process in the operating system, and it is also  called a task control block. Each process must have one PCB because the operating system need the information of the process to to the manipulation of all the process. And those information is stored in the PCB, for example, the process state, process number, program counter and registers are very important when the operating system is executing all the process and when interruptions occurs.