Q30.Marks: +2.0UGC NET Paper 2: Computer Science 11 March 2023
Consider an operating system capable of loading and executing a single sequential user process at a time. The disk head scheduling algorithm used is first come first served (FCFS). If FCFS is replaced by shortest seek time first (SSTF) and the vendor claims 50% better benchmark results. What is the expected improvement in the I/O performance of user programs?
1.50%
2.100%
3.25%
4.0%✓ Correct
Solution
The correct answer is 0%
Key Points
While the disk head scheduling algorithm can make a huge difference in the performance of the disk I/O operations, it does not have a direct impact on the execution of user programs. The performance of user programs depends mainly on the CPU scheduling policies and the available resources such as main memory, cache, and so on.
Switching from FCFS to SSTF only makes the disk drive work better, but it doesn't improve the overall performance of the user program with various input and output devices. In simple terms, the user program's I/O performance stays the same, with no improvement (0% improvement).
Additional Information
FCFS (First-Come, First-Served): FCFS is a scheduling algorithm that services tasks in the order they arrive. The first to arrive gets served first. It's simple but can lead to high waiting times if a long task arrives before short tasks.
SSTF (Shortest Seek Time First): SSTF is a disk scheduling algorithm that services the disk I/O request closest to the current position of the disk head, thereby minimizing total seek time. It's typically more efficient than FCFS, but can lead to starvation of some requests.
