Key Points: Scheduling Algorithms
First Come, First Served (FCFS)
- Definition: Processes are executed in the order they arrive
- Characteristics:
- Simple to implement
- Non-preemptive
- Can lead to long average wait times, especially if long processes arrive first
Shortest Job First (SJF)
- Definition: Process with the shortest execution time is selected to run next
- Characteristics:
- Optimal for minimizing average wait time
- Requires knowing or estimating job lengths in advance
- Can lead to starvation of longer processes
Round Robin (RR)
- Definition: Each process is given a fixed time quantum to execute before being preempted
- Characteristics:
- Preemptive
- Fair allocation of CPU time
- Good response time but processes take longer to complete
- Performance depends on choice of quantum
- Introduces context switch overhead
Scheduling Metrics
- Response Time: Time from when a process arrives until it first gets CPU time
- Turnaround Time: Time from when a process arrives until it completes
- Wait Time: Total time a process spends waiting in the ready queue
Context Switches
- Definition: The process of saving the state of a running process and loading the state of another
- Impact: Introduces overhead, affecting overall system performance
Remember
- Each scheduling algorithm has its own strengths and weaknesses
- There's no "one size fits all" solution in scheduling; the best algorithm depends on the specific use case
- Understanding trade-offs between metrics (response time, turnaround time, wait time) is crucial
- Context switches are an important consideration in preemptive scheduling
- Be prepared to draw charts showing how processes are scheduled under different algorithms—it's a classic exam question!
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