1 What is a Process ? The activity of program execution. Also called a task or job Has associated with it: Code Data Resources A State An executing set of machine instructions

2 When is a Process Created? Principal events that cause process creation 1.System initialization Execution of a process creation system 1.User request to create a new process 2.Initiation of a batch job

3 The resources ‘owned’ by the process include: the (virtual) Address Space to hold the process image and may include control of other resources such as Main memory I/O channels I/O devices Files

4 What are the Operating System Responsibilities for Processes? Interleave the execution of several processes to maximize processor utilization while providing reasonable response time Allocate resources to processes Support interprocess communication and user creation of processes

5 Conceptual model of 4 independent, sequential processes Multiprogramming of four programs Only one program active at any instant

6 OS Handling Processes in a Multiprogrammed System

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9 Process States and Transitions between States

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11 Fields of a Process Control Block or Table

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13 Process Termination Conditions 1.Normal exit (voluntary) - job completed. 2.Error exit (voluntary) - occurs within execution of process such as division by zero but process may be just signaled and not terminated. 3.Fatal error (involuntary) - impossible for process to continue. Ex. Cc file.c process called but file.c does not exist. 4.Killed by another process (involuntary)

14 Process Hierarchies Parent creates a child process, child processes can create its own process Forms a hierarchy –UNIX calls this a "process group” –when a signal is sent from the keyboard, each process in the group receives the signal. –all processes belong to a single tree with the special process ‘init’ at the root. ‘init’ is in the boot. Windows has no concept of process hierarchy –all processes are created equal