Session 1 Introduction-1.ppt - ICS 2202 Operating Systems I...

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Process Management Part 1 ICS 2202 Operating Systems I 1 ICS 2202 Operating Systems I
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Introduction ICS 2202 Operating Systems I 2 Process management entails two key issues: Ensure each process receives enough processor time to function. Have as many useful processor cycles as possible .
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Introduction ICS 2202 Operating Systems I 3 The term "process" was first used by the designers of the MULTICS in 1960's. Since then, the term process, used somewhat interchangeably with 'task' or 'job'. The process has been given many definitions for instance: A program in Execution. An asynchronous activity. The 'animated split' of a procedure in execution. The entity to which processors are assigned. The 'dispatchable' unit. There is no universally agreed upon definition, but the definition " Program in Execution " seem to be most frequently used. And this is a concept we will use in the present study of operating systems.
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Process vs Program ICS 2202 Operating Systems I 4 It is the same beast with different name when this beast is sleeping (not executing) it is called program and when it is executing becomes process. A process is an 'active' entity as opposed to program which consider to be a 'passive' entity. A Process includes: Current value of Program Counter (PC) Contents of the processors registers Value of the variables The process stack (SP) which typically contains temporary data such as subroutine parameter, return address, and temporary variables. A data section that contains global variables.
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Process vs Program ICS 2202 Operating Systems I 5 In Process model, all software on the computer is organized into a number of sequential processes. A process includes PC, registers, and variables. Conceptually, each process has its own virtual CPU. In reality, the CPU switches back and forth among processes. (The rapid switching back and forth is called multiprogramming).
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Process Operations ICS 2202 Operating Systems I 6 Process Creation In general-purpose systems, some way is needed to create processes as needed during operation. There are four principal events lead to process creation. System initialization. Creation of a child process invoking fork() system call by a running process. A user request to create a new process. Initialization of a batch job. Operating systems creates process to provide service, e.g., to manage printer.
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ICS 2202 Operating Systems I 7 Foreground processes interact with users. Background processes stay in background sleeping but may suddenly spring up to life to handle activity such as email, webpage, printing, and so on. Background processes are called daemons. This call creates an exact clone of the calling process. A process may create a new process by some create process cmd such as 'fork'. The creating process is called parent process and the created one is called the child processes. Only one parent is needed to create a child process. Note that unlike plants and animals that use sexual representation, a process has only one parent.
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