Which of the following is not a CPU scheduling Algorithm?
C-SCAN
Understanding CPU Scheduling Algorithms
CPU scheduling is a process where the operating system decides which process gets to use the CPU next and for how long. The goal is to improve system performance by utilizing the CPU efficiently and providing good response times for users. There are many different CPU scheduling algorithms, each with its own advantages and disadvantages.
Let's look at the options provided and determine which one is not a CPU scheduling algorithm.
Analyzing the Given Options
- C-SCAN: This stands for Circular SCAN. C-SCAN is a disk scheduling algorithm, not a CPU scheduling algorithm. Disk scheduling algorithms determine the order in which disk I/O requests are serviced to minimize the seek time and improve overall disk access performance. C-SCAN moves the disk head in one direction, servicing requests until it reaches the end of the disk or the last request in that direction, then it jumps back to the beginning of the disk without servicing any requests on the return trip and starts moving again in the same direction.
- FCFS: This stands for First-Come, First-Served. FCFS is a CPU scheduling algorithm. It is the simplest scheduling algorithm, where processes are executed in the order they arrive in the ready queue.
- SJF: This stands for Shortest Job First. SJF is a CPU scheduling algorithm. It schedules processes based on the length of their next CPU burst. The process with the smallest next CPU burst is executed first.
- SJN: This stands for Shortest Job Next. SJN is another name for the Shortest Job First (SJF) CPU scheduling algorithm. It operates on the same principle as SJF.
Distinguishing CPU Scheduling vs. Disk Scheduling
It's important to differentiate between CPU scheduling and disk scheduling, as they address different resources and goals:
| Feature | CPU Scheduling | Disk Scheduling |
|---|---|---|
| Resource Managed | Central Processing Unit (CPU) | Hard Disk Drive (HDD) or Solid State Drive (SSD) |
| Goal | Maximize CPU utilization, minimize response time, minimize waiting time, maximize throughput. | Minimize head movement (seek time), optimize data access speed, improve I/O performance. |
| Algorithms Examples | FCFS, SJF, Priority Scheduling, Round Robin, Multilevel Queue Scheduling | FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK |
Based on the analysis, FCFS, SJF, and SJN (which is SJF) are all well-known CPU scheduling algorithms. C-SCAN, however, belongs to the category of disk scheduling algorithms.
Conclusion
Therefore, C-SCAN is the option that is not a CPU scheduling algorithm.
Revision Table: Scheduling Algorithms
| Algorithm Name | Type | Description |
|---|---|---|
| FCFS (First-Come, First-Served) | CPU Scheduling | Processes are executed in arrival order. |
| SJF (Shortest Job First) | CPU Scheduling | Processes with the shortest next CPU burst are executed first. |
| SJN (Shortest Job Next) | CPU Scheduling | Another name for SJF. |
| C-SCAN (Circular SCAN) | Disk Scheduling | Disk head moves in one direction, wraps around to the beginning after reaching the end or last request. |
Additional Information: Types of CPU Scheduling
CPU scheduling can be broadly categorized into two types:
- Preemptive Scheduling: In this type, a running process can be interrupted and moved back to the ready queue if a higher priority process arrives or if its time slice expires. Examples include Round Robin, Priority Scheduling (preemptive), SJF (preemptive).
- Non-Preemptive Scheduling: In this type, once a process starts executing, it continues until it completes its CPU burst or blocks for I/O. It cannot be interrupted by other processes. Examples include FCFS, SJF (non-preemptive), Priority Scheduling (non-preemptive).
Disk scheduling algorithms like C-SCAN are designed specifically for managing the movement of the disk head to access data blocks, minimizing the time spent seeking different tracks on the disk platter.
Important Questions from Process Scheduling - Teaching
Consider the following 3 processes with the length of the CPU burst time given in milliseconds :
Process Arrival Time Burst Time P1 0 8 P2 1 4 P3 2 9 What is the average waiting time for these processes if they are scheduled using preemptive shortest job first scheduling algorithm?
Consider the following four processes with the arrival time and length of CPU burst given in milliseconds :
Process Arrival Time Burst Time P 1 0 8 P 2 1 4 P 3 2 9 P 4 3 5 The average waiting time for preemptive SJF scheduling algorithm is
Which of the following statement(s) is/are true about CPU scheduling algorithm?
I. Shortest remaining time first scheduling may cause starvation
II. Round Robin is better than First Come First Serve in terms of response time
Processes P1, P2, P3 and P4 have CPU burst times 5, 7, 6 and 4 ms, respectively. All arrive at time 0, and the initial ready-queue order is P1, P2, P3, P4. Using Round-Robin scheduling with a 4 ms time quantum and no context-switch overhead, what is P4’s total waiting time in milliseconds?
A process residing in main memory and ready and waiting for execution, is kept on
