1. What is the purpose of Process?

From a theoretical point of view, it is an abstraction of the running program process; From an implementation perspective, it is a data structure whose purpose is to clearly describe the internal laws of a dynamic system, and effectively manage and schedule programs that enter the main memory of the computer system.

2. describe their relation and difference for process and program.

The essence of the process is the one-time execution of the program in the multi-program system. The process is dynamically generated and died dynamically. Any process can execute concurrently with other processes. A process is a basic unit that can run independently, as well as an independent unit for system resource allocation and scheduling. Due to the mutual constraints between the processes, the processes have intermittent execution, that is, the processes advance at an independent and unpredictable speed. The process consists of three parts: program, data and process control block;

3. Why the status of process is divided into five states, not other number, such as 4.7?

A process in the running state will enter the waiting state due to a waiting event. When the waiting event ends, the process in the waiting state will enter the ready state, and the processor's scheduling strategy will cause a switch between the running state and the ready state.So we have five status: new\exit\running\ready\blocked, corresponding to different state switching of the process.