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Friday, August 16, 2013

PPT On Process Description and Control


Process Description and Control Presentation Transcript:
1.Process Description and Control

2.Requirements of an Operating System
Interleave the execution of multiple processes to maximize processor utilization while providing reasonable response time
Allocate resources to processes
Support inter process communication and user creation of processes

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

4.Manage Execution of Applications
Resources made available to multiple applications
Processor is switched among multiple application
The processor and I/O devices can be used efficiently

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

6.Process Elements
Program counter
Memory pointers
Context data
I/O status information
Accounting information

7.Process Control Block
Contains the process elements
Created and manage by the operating system
Allows support for multiple processes

8.Process Control Block

9.Trace of Process
Sequence of instruction that execute for a process
Dispatcher switches the processor from one process to another

10.Example Execution

11.Two-State Process Model
Process may be in one of two states

12.Not-Running Process in a Queue

ready to execute
waiting for I/O
Dispatcher cannot just select the process that has been in the queue the longest because it may be blocked

14.A Five-State Model

15.Suspended Processes is faster than I/O so all processes could be waiting for I/O
Swap these processes to disk to free up more memory
Blocked state becomes suspend state when swapped to disk
Two new states
Ready Suspend

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