GATE CS 1999 Q1.10 — I/O Scheduling

To maximize disk throughput, a disk scheduling algorithm must minimize the average seek time, as seek time is the most significant overhead in disk I/O operations.

Let's evaluate the given strategies:

• Nearest Cylinder Next (Shortest Seek Time First - SSTF): This strategy always services the request closest to the current head position. By greedily minimizing the seek distance for each step, it minimizes the total seek time, thereby yielding the highest throughput among the standard algorithms (though it can potentially cause starvation for requests far from the head).
• Elevator Algorithm (SCAN): The head moves in one direction servicing requests until it reaches the end, then reverses. While it prevents starvation and provides a more uniform waiting time, its throughput is generally slightly lower than SSTF because it does not always service the absolute closest request first if it lies in the opposite direction of travel.
• First Come First Served (FCFS): Services requests in the order they arrive. This is fair but results in random head movements, leading to high seek times and low throughput.
• Farthest Cylinder Next: This is highly inefficient as it maximizes seek times, resulting in the worst possible throughput.

Therefore, Nearest cylinder next is likely to give the best throughput.