In the process control block, it mainly includes the following information

　　(1) Process identifier: The process identifier is used to uniquely represent a process. A process usually has two kinds of identifiers: ① external identifier. In order to facilitate the access of the user process to the process, an external identifier must be set for each process. It is provided by the creator and usually consists of letters and numbers. In order to describe the family relationship of the process, the parent process ID and the child process ID should also be set. In addition, a user ID can be set to indicate the user who owns the process. ② Internal identifier. In order to facilitate the use of the process by the system, an internal identifier is set for the process in the OS, that is, a unique numerical identifier is given to each process, which is usually the sequence number of a process.

　　(2) Processor state: The processor state information is also called the context of the processor, which is mainly composed of the contents of various registers of the processor. These registers include: ① General-purpose registers, also known as user-visible registers, which can be accessed by user programs and are used to temporarily store information. In most processors, there are 8 to 32 general-purpose registers. There can be more than 100 in it; ② instruction counter, which stores the address of the next instruction to be accessed; ③ program status word PSW, which contains status information, such as condition code, execution mode, interrupt mask flag, etc.; ④ user stack pointer, It means that each user process has one or several system stacks associated with it, which are used to store process and system call parameters and call addresses. The stack pointer points to the top of the stack. While the processor is executing, much of the information being processed is placed in registers. When the process is switched, the processor state information must be saved in the corresponding PCB, so that the process can resume execution from the breakpoint when the process is re-executed.

　　(3) Process scheduling information: When the OS performs scheduling, it is necessary to know the state of the process and information about process scheduling. These information include: ① Process state, which indicates the current state of the process, which is used as the basis for process scheduling and swapping ; ② Process priority is an integer used to describe the priority level of the process using the processor, and the process with higher priority should get the processor first; ③ Other information required for process scheduling, which is related to the process scheduling algorithm used , for example, the sum of the time the process has waited for the CPU, the sum of the time the process has executed, etc.; ④ Event refers to the event waiting for the process to change from the execution state to the blocking state, that is, the blocking reason.

　　(4) Process control information: It refers to the information necessary for process control, which includes: ① the address of the program and data, the memory or external memory address of the program and data in the process entity, so as to be re-scheduled to the execution of the process. , can find its program and data from the PCB; ② process synchronization and communication mechanism, which is a necessary mechanism to achieve synchronization and process communication, such as message queue pointers, semaphores, etc., which may be placed in the PCB in whole or in part; ③Resource list, in which all resources (except CPU) required by the process during operation are listed, and there is also a list of resources allocated to the process; ④Link pointer, which gives the process ( PCB) is the first address of the PCB of the next process in the queue.

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