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Process Concepts

Definition

  • One execution of a program: A process can be regarded as an instance of program execution.

  • Active process: A process is an activity that occurs when a program and its data are executed sequentially on a processor.

  • Resource management and scheduling unit: A process is a process in which a program with independent functions runs on a data set, and is an independent unit of system resource allocation and scheduling.

Composition

  • Program Control Block (PCB): Contains information required by the operating system to manage processes, including process description information, control and management information, resource allocation list, and processor related information.

  • Program segment: An area used to store program code.

  • Data segment: Stores data used or generated when a program is running, such as global variables, local variables, and macro-defined constants.

  • Process image: The whole composed of program control block, program segment, and data segment is called process image.

Process characteristics

  • Dynamicity: The most basic characteristic of a process, indicating that it is a dynamic process, from generation to change to extinction.

  • Concurrency: Multiple processes can exist in memory, and these processes can be executed concurrently.

  • Independence: Processes can run independently, obtain resources independently, and serve as independent scheduling units.
  • Asynchrony: Each process advances at its own speed, and the operating system provides a synchronization mechanism to solve the asynchronous problem.
  • Structural: Structurally, a process consists of a program segment, a data segment, and a program control block (PCB), collectively referred to as a "process image."