2. Goal of OS:
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An operating system is the framework that allows you to communicate with computer hardware in an interactive way. Without this, you would not be able to tell the computer to do anything and it would have any instructions to follow. This is why it is important for a computer to have an operating system .In early days without OS so much problems where faced like acessing or getting output it takes two days. To make it much more efficient OS is used.
§Interleave the execution of the number of processes to maximize processor utilization while providing reasonable response time
§The main idea of scheduling:
The system decides:
¨ Who will run
¨ When will it run
¨ For how long
In order to achieve its goals
Quality criteria for scheduling (algorithm)
§ Fairness: each process gets a “fair share” of the cpu
§ Efficiency: “keep the cpu busy”
§ Response time: minimize, for interactive users
§ Turnaround: for batch users (total time of batch)
§ Throughput: maximal number of processed jobs per unit time
§ Waiting time: minimize the average over processes
Scheduling – quality measures
§Throughput – number of processes completed per unit time
§ Turnaround time – interval of (real) time from process submission to completion
§ Waiting time – sum of time intervals the process spends in the ready queue
§ Response time – the time between submitting a command and the generation of the first output
§ CPU utilization – the part of the total (elapsed) time, the cpu is computing some process – between 0 and 100%
Conflicting Goals
§Response Time vs Turnaround time:
A conflict between:
Interactive and batch users.
§ Fairness vs Throughput:
Consider a very long job.
should it be run?
§Interleave the execution of the number of processes to maximize processor utilization while providing reasonable response time
§The main idea of scheduling:
The system decides:
¨ Who will run
¨ When will it run
¨ For how long
In order to achieve its goals
Quality criteria for scheduling (algorithm)
§ Fairness: each process gets a “fair share” of the cpu
§ Efficiency: “keep the cpu busy”
§ Response time: minimize, for interactive users
§ Turnaround: for batch users (total time of batch)
§ Throughput: maximal number of processed jobs per unit time
§ Waiting time: minimize the average over processes
Scheduling – quality measures
§Throughput – number of processes completed per unit time
§ Turnaround time – interval of (real) time from process submission to completion
§ Waiting time – sum of time intervals the process spends in the ready queue
§ Response time – the time between submitting a command and the generation of the first output
§ CPU utilization – the part of the total (elapsed) time, the cpu is computing some process – between 0 and 100%
Conflicting Goals
§Response Time vs Turnaround time:
A conflict between:
Interactive and batch users.
§ Fairness vs Throughput:
Consider a very long job.
should it be run?
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