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Operating System Structures & Processes

This lecture covers the design goals, implementation methods, and concepts related to processes in operating systems. The slides are based on the textbook "Operating Systems Concepts with Java". Topics include process states, process control block, process scheduling, and queues.

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Operating System Structures & Processes

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  1. Operating System Structures&Processes Notice: The slides for this lecture have been largely based on those accompanying the textbook Operating Systems Concepts with Java, by Silberschatz, Galvin, and Gagne (2003). Many, if not all, the illustrations contained in this presentation come from this source. CSCI 315 Operating Systems Design

  2. Operating System Design Goals • User goals – operating system should be convenient to use, easy to learn, reliable, secure, and fast. • System goals – operating system should have a simple design, be easy to implement, and maintain, as well as be flexible, reliable, error-free, and efficient. CSCI 315 Operating Systems Design

  3. System Implementation • Traditionally written in assembly language, operating systems can now be written in higher-level languages. • Code written in a high-level language: • Can be written faster, • Is more compact, and • Is easier to understand and debug. • An operating system is far easier to port (move to some other hardware) if it is written in a high-level language. CSCI 315 Operating Systems Design

  4. Chapter 3Processes CSCI 315 Operating Systems Design

  5. Process Concept heap • Process – a program in execution; process execution must progress in sequential fashion. • A process includes: • program counter, • stack, • data section. stack data code program counter CSCI 315 Operating Systems Design

  6. Process State As a process executes, it changes state: • new: The process is being created. • running: Instructions are being executed. • waiting: The process is waiting for some event to occur. • ready: The process is waiting to be assigned to a processor. • terminated: The process has finished execution. CSCI 315 Operating Systems Design

  7. Process State Transition Diagram terminated exit new admitted interrupt running ready scheduler dispatch I/O or event completion I/O or event wait waiting CSCI 315 Operating Systems Design

  8. Process Control Block (PCB) OS bookkeeping information associated with each process: • Process state, • Program counter, • CPU registers, • CPU scheduling information, • Memory-management information, • Accounting information, • I/O status information, process id process state program counter registers memory limits list of open files CSCI 315 Operating Systems Design

  9. CPU Switching CSCI 315 Operating Systems Design

  10. Process Scheduling Queues • Job queue – set of all processes in the system. • Ready queue – set of all processes residing in main memory, ready and waiting to execute. • Device queues – set of processes waiting for an I/O device. Processes migrate between the various queues. CSCI 315 Operating Systems Design

  11. Processes and OS Queues CSCI 315 Operating Systems Design

  12. Process Scheduling CPU ready queue I/O I/O queue I/O request time slice expired child executes fork a child interrupt occurs wait for interrupt CSCI 315 Operating Systems Design

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