1. 3.1 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q:Process Stateu 有哪些 ? 何種情形下會做 transition? 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

2. 3.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q: 所謂 context 主要是包含哪些資料 ? 或問所謂 PCB 主要是包含哪些資料 ? Information associated with each process Process state Program counter CPU registers CPU scheduling information Memory-management information Accounting information I/O status information

3. 3.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q: 何謂 Context Switch? When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process via a context switch Context of a process represented in the PCB Context-switch time is overhead; the system does no useful work while switching Time dependent on hardware support

4. 3.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q:(a) 簡單說明 OS 如何由 process A 到 B 做 context switching?

5. 3.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q:Describe the difference among short-term, medium-term, and long-term scheduling? Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU

6. 3.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Addition of Medium Term Scheduling

7. 3.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Schedulers (Cont) Short-term scheduler is invoked very frequently (milliseconds)  (must be fast) Long-term scheduler is invoked very infrequently (seconds, minutes)  (may be slow) The long-term scheduler controls the degree of multiprogramming

8. 3.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q: 說明 I/O-bound process & CPU-bound process? Processes can be described as either: I/O-bound process – spends more time doing I/O than computations, many short CPU bursts CPU-bound process – spends more time doing computations; few very long CPU bursts

9. 3.9 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q: 何謂 Interprocess Communication? 可能 方法 ? Processes within a system may be independent or cooperating Cooperating process can affect or be affected by other processes, including sharing data Reasons for cooperating processes: Information sharing Computation speedup Modularity Convenience Cooperating processes need interprocess communication (IPC) Two models of IPC Shared memory Message passing

10. 3.10 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Communications Models

11. 3.11 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Q:Blocking (TRX) vs nonblocking? Message passing may be either blocking or non-blocking Blocking is considered synchronous Blocking send has the sender block until the message is received Blocking receive has the receiver block until a message is available Non-blocking is considered asynchronous Non-blocking send has the sender send the message and continue Non-blocking receive has the receiver receive a valid message or null