1007ICT Computer Systems and Networks WS9 PDF

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Workshop 9 Operating System Notes...

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1007ICT: Computer Systems and Networks Workshop 9: Operating Systems 1. List 3 CPU scheduling strategies ● First-come first served: The scheduler dispatches the ready process that has been waiting the longest. ● Explicit priority: Each process can be assigned a priority level. The scheduler dispatches the ready process that has the highest assigned priority level. ● Shortest Remaining Time: The next process to be dispatched is based on the expected amount of CPU time needed to complete the process. 2. List 3 steps that the dispatcher performs ● Dispatching is the task of switching between processes. ● The process's context or volatile portion is the information that defines a process and is contained in a CPU’s registers. ● The Operating System saves the process context of the running process to the stack, then the saved context of the next process from the ● This is called contextswitching

loads stack.

3. Describe the difference between pre-emptive and non-pre-emptive scheduling ● An OS may run several processes concurrently but each must take turns at accessing the CPU ● Some OS’s allow each process to decide when it wants to let another process access the CPU. This is non-preemptive scheduling ● In contrast, a pre-emptive operating system can interrupt a process and force it to yield to another process ● Pre-emptive scheduling ○ Interleaves processes based on a timer and process priority ○ Interrupts generated by the timer are used to involuntarily remove the running process from the running state ○ The scheduler then dispatches one of the other processes that is in a ready state (not blocked) ○ I/O requests are interrupt driven, that is when a process wants to do an I/O function it generates an interrupt...