The PCB process control block is a static description of the process, which consists of three parts: PCB, related program segments and data structure sets for program segment operations.

In a Unix or Unix-like system, a process consists of the process control block, the programs that the process executes, the data that the process uses to execute, and the work area that the process uses to run. The process control block is the most important part.

A process control block is a data structure that describes the current state of a process and its own characteristics. This is the most critical part of the process. It contains descriptive process information and control information. It is a concentrated characterization of the process. Basis for identification and control.

PCBs usually include:

1. Program ID (PID, process handle): unique, a process must correspond to a PID. PID is generally an integer

2. Characteristic information: Generally, it is a subsystem process, a user process, or a kernel process, etc.

3. Process status: running, ready, blocked, indicating the current running status of the process

4. Priority: Indicates the priority of obtaining CPU control

5. Communication information: a reflection of the communication relationship between processes, because the operating system will provide communication channels

6. Site Sanctuary: Protect blocked processes

7. Resource requirements, allocation control information

8. Process entity information, indicating the program path and name, whether the process data is in physical memory or in the swap partition (paging)

9. Other information: work unit, work area, file information, etc.