the life circle of process

A process life includes five states: New, Running, Waiting, Ready and Terminated. Those states have their own meaning. For example:

New: The process is being created

Running: Instruction are being executed

Waiting: The process is waiting for some event to occur(such as an I/O completion or reception of signal)

Ready: The process is waiting to be assigned to a processor

Terminated: The process has finished execution

And durning the process's life, it will transparent from one state to others when specific situation is fitted.
why each process must have one PCB Each PCB contains import information about a process such as it's process state, program counter, cpu register, cpu-scheduling information, memory-management information, accounting information, I/O status information and every thing else about the process which must be saved when the process is interrupted or switch from running to ready or waiting. So when the process restart later, it return the state before change.