lecture3 - Lecture 3 Processes Threads(Part 1 of 3...

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Defintion of Process We’restarting with CPU as a resource, so we need an abstraction of CPU ues. We define a process as the OS’srepresentation of a program in execution so that we can allocate CPU time to it. (Other defs: “the thing pointed to by a PCB” to “the animated spirit of a procedure”). Note the difference between a program and a process. The ls program on disk is a program; the ls instance running on a computer is a process. Multiple processes can be running the same program. The process abstraction turns out to be convenient to hang other resource allocations on. File system usage (disk/tape), memory usage, network usage, and number of subprocesses (i.e. further CPU utilization) are all assigned on a per-process basis. Processes are the unit of isolation. Tw o processes cannot directly affect each other’sbehavior with- out making explicit arrangements to. This isolation extends itself to more general security concerns. Pro- cesses are tied to users, and the credentials from running on a user’sbehalf determine what resources the process can use. Process Operatons and Attributes Processes can be created and destroyed. Becuase the’re created or destroyed by the CPU, theyare created or destroyed by other processes. Because of this OS designers speak of parent and child processes (the parent being the creator and the child being the creation).
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This note was uploaded on 02/28/2008 for the course CS 402 taught by Professor Tedfaber during the Spring '05 term at USC.

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lecture3 - Lecture 3 Processes Threads(Part 1 of 3...

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