Chapter 3 - Process description and control. This chapter refers to virtual memory. Much of the time, we can ignore this concept in dealing with processes, but at certain points in the discussion, virtual memory considerations are pertinent. | Chapter 3 Process Description and Control What is a process? Process states which characterize the behaviour of processes. Data structures used to manage processes. Ways in which the OS uses these data structures to control process execution. Requirements of an Operating System Fundamental Task: Process Management The Operating System must Interleave the execution of multiple processes Allocate resources to processes Protect the resources of each process from other processes Enable processes to share and exchange information Enable synchronization among processes. What is a “process”? A program in execution An instance of a program running on a computer The entity that can be assigned to and executed on a processor A unit of activity characterized by the execution of a sequence of instructions, a current state, and an associated set of system resources Process Elements A process is comprised of: Program code (possibly shared) A set of data associated with the code A number | Chapter 3 Process Description and Control What is a process? Process states which characterize the behaviour of processes. Data structures used to manage processes. Ways in which the OS uses these data structures to control process execution. Requirements of an Operating System Fundamental Task: Process Management The Operating System must Interleave the execution of multiple processes Allocate resources to processes Protect the resources of each process from other processes Enable processes to share and exchange information Enable synchronization among processes. What is a “process”? A program in execution An instance of a program running on a computer The entity that can be assigned to and executed on a processor A unit of activity characterized by the execution of a sequence of instructions, a current state, and an associated set of system resources Process Elements A process is comprised of: Program code (possibly shared) A set of data associated with the code A number of attributes describing the state of the process Process Elements While the process is running, it has a number of attributes including Identifier State Priority Program counter Memory pointers Context data I/O status information Accounting information Trace of the Process The behavior of an individual process is shown by listing the sequence of instructions that are executed This list is called a Trace Dispatcher is a small program which switches the processor from one process to another Process Execution Consider three processes being executed All are in memory (plus the dispatcher) Trace from the Process point of view: The 4th instruction of Process B invokes an I/O operation. Trace from Processor’s point of view Timeout I/O Timeout Timeout Time slice: 6 instruction cycles Roadmap What is a process? Process states which characterize the behaviour of processes. Data structures used to manage processes. Ways in which the OS uses these data structures to .
