1.A process has five states: new, running, waiting, ready, terminated.

The life circle of  process starts when it is created. When it is allowed, it will be ready. The process in the ready state is allocated by the scheduling algorithm to run. When the running process receives the exit instruction, it enters the termination state, and the process ends. The running process will also receive I/O operation or event waiting requirements, thus entering the waiting state. When I/O operations and events are completed, the process is ready for the next instruction. Running processes are also ready to receive interrupt instructions.

2.Each process will occupy CPU. In order to control each process and realize CPU switching between processes, each process need to be controlled by a PCB