Scheduling Criteria | CPU Utilization | Throughput | Turnaround time | Waiting time | Response time

Scheduling:

 Scheduling is a process which allows one process to use the CPU while the execution of another process is on hold (in waiting state) due to unavailability of any resource like I/O etc. 2. The aim of scheduling is to make the system efficient, fast and fair. Scheduling Criteria: I) CPU Utilization:
 To make out the best use of CPU and not to waste any CPU cycle, CPU would be working most of the time (Ideally 100% of the time).  Considering a real system, CPU usage should range from 40% (lightly loaded) to 90% (heavily loaded)  Keep the CPU Busy as much as possible.
II) Throughput:
 The number of process executed by the system in a specific period of time, this time unit is called through put.  For long process this rate may be one process per minute.  Similarly for short process, it may be 100 processes per minute.  The evaluation of through must be considered on the basis of average length.
III) Turnaround time:
 Turnaround time represents the average period of time taken by a process executes.  The turnaround time is computed by subtracting the time, when the process was created from the time is terminated.  The turnaround time is inversely proportional to through put.
IV) Waiting time:
 Waiting time represents the average period of time, a process spends waiting in the ready queue to get a chance for execution.  It does not include the time, a process is executing on the CPU or performing I/O.  Waiting time is also very important factor to measure the performance of the system.
V) Response time:
 Response time represents the average time take by the system to start responding to user request.  The response time is considered in interactive systems.  For example, ATM is an interactive system, which is used in banks for withdrawal of money.  The user expects that the system should response quickly.  Response time in an interactive system should be very less.
In general CPU utilization and Throughput are maximized and other factors are reduced for proper optimization.

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