1.Process is the unit of resource encapsulation and management. Resource refers to the occupied memory, file system, signal and processing methods.Operating system includes real-time system corresponding process, which generally has three states. Processes correspond to running state with CPU, ready state and sleeping state without CPU. Readiness means that all resources are ready to run as long as there is a CPU. Sleep means that resources are not ready, for example, when reading serial data, the data is not sent. At this time, the CPU can not run. It needs to wait until the resources are ready to become ready, and then get the CPU before it can become operational.

2.In the whole life cycle of a process, the system always controls the process through its PCB. The system perceives the existence of the process according to the PCB of the process, not anything else. So, every process must have a PCB.