Ready state: The process has acquired all other resources except the cpu, waiting for the CPU to schedule in the ready queue
Execution status: the CPU has been obtained and all required resources are running
Blocking state (waiting state): A process abandons the processor or process book because it waits for the required resources.
To have no processor, and other resources are not satisfied

why each process must have one PCB
The function of PCB is to make a program (including data) that can\'t run independently in multi-programming environment become a basic unit that can run independently and a process that can run concurrently with other processes. In other words, the operating system controls and manages concurrently executed processes according to PCB, which is the only identification of the existence of processes.