In this chapter we introduce the concept of a process and the notion of concurrent execution. Those are at the very heart of modern operating systems. A process is is a program in execution and is the unit of work in a modern time-sharing system. Such a system consists of a collection of processes: Operating-system processes executing system code, and user processes executing user code. This chapter also discuss the notion of a thread (light-weight process) and interprocess communication (IPC). | Module 4: Processes Process Concept Process Scheduling Operation on Processes Cooperating Processes Interprocess Communication Operating System Concepts Process Concept An operating system executes a variety of programs: Batch system – jobs Time-shared systems – user programs or tasks Textbook uses the terms job and process almost interchangeably. Process – a program in execution; process execution must progress in sequential fashion. A process includes: program counter stack data section Operating System Concepts Process State As a process executes, it changes state new: The process is being created. running: Instructions are being executed. waiting: The process is waiting for some event to occur. ready: The process is waiting to be assigned to a process. terminated: The process has finished execution. Operating System Concepts Diagram of Process State Operating System Concepts Process Control Block (PCB) Information associated with each process. Process state Program counter CPU . | Module 4: Processes Process Concept Process Scheduling Operation on Processes Cooperating Processes Interprocess Communication Operating System Concepts Process Concept An operating system executes a variety of programs: Batch system – jobs Time-shared systems – user programs or tasks Textbook uses the terms job and process almost interchangeably. Process – a program in execution; process execution must progress in sequential fashion. A process includes: program counter stack data section Operating System Concepts Process State As a process executes, it changes state new: The process is being created. running: Instructions are being executed. waiting: The process is waiting for some event to occur. ready: The process is waiting to be assigned to a process. terminated: The process has finished execution. Operating System Concepts Diagram of Process State Operating System Concepts Process Control Block (PCB) Information associated with each process. Process state Program counter CPU registers CPU scheduling information Memory-management information Accounting information I/O status information Operating System Concepts Process Control Block (PCB) Operating System Concepts CPU Switch From Process to Process Operating System Concepts Process Scheduling Queues Job queue – set of all processes in the system. Ready queue – set of all processes residing in main memory, ready and waiting to execute. Device queues – set of processes waiting for an I/O device. Process migration between the various queues. Operating System Concepts Ready Queue And Various I/O Device Queues Operating System Concepts Representation of Process Scheduling Operating System Concepts Schedulers Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue. Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU. Operating System Concepts Addition of Medium Term Scheduling Operating System Concepts Schedulers .
