The life circle of a progress could be divided into 6 parts in detail.

1.task_zombie:The process has ended but the PCB has not been released.

2.task_uninterruptible :Sleep processes that are disabled due to kernel instructions. It can not be wakened by external signals, but by the kernel itself.

3.task_interruptible: Set for sleep processes waiting for an event or other resource. When a signal from the kernel to the process surface event has occurred, the process state changes to TASK_RUNNING, and it can resume execution as long as the scheduler selects the process.

4.task_stopped:The process suspends execution and accepts some sort of processing.

5.task_ready:Unoccupied CPU, waiting for the scheduling algorithm to schedule to the running process

6.task_running:Holding CPU, running thread.

Why PCB:

1.PCB is a part of the process entity and the most important data structure in the operating system.
2.Because of its existence, the program that can not run independently becomes a basic unit that can run independently in the multi-channel environment, so that the program can be executed concurrently.
3.PCB is the unique identifier for the existence of a process..