聊城大学计算机学院计算机操作系统（1）英文课件 Chapter3.ppt

Process Description and Control Chapter 3 Requirements of anOperating System Interleave the execution of multiple processes to maximize processor utilization while providing reasonable response time Allocate resources to processes Support interprocess communication and user creation of processes Concepts Computer platform consists of a collection of hardware resources Computer applications are developed to perform some task Inefficient for applications to be written directly for a given hardware platform Operating system provides a convenient to use, feature rich, secure, and consistent interface for applications to use OS provides a uniform, abstract representation of resources that can be requested and accessed by application Manage Execution of Applications Resources made available to multiple applications Processor is switched among multiptle application The processor and I/O devices can be used efficiently 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 instructions Process Elements Identifier State Priority Program counter Memory pointers Context data I/O status information Accounting information Process Control Block Contains the process elements Created and manage by the operating system Allows support for multiple processes Process Control Block Trace of Process Sequence of instruction that execute for a process Dispatcher switches the processor from one process to another Example Execution Trace of Processes Two-State Process Model Process may be in one of two states Running Not-running Not-Running Process in a Queue Process Creation Process Termination Process Termination Processes Not-running ready to execute Blocked waiting for I/O Dispatcher cannot just select the process that has been in the queue the longest because it may be bloc