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?

Explanation

Disk-scheduling algorithms like SSTF only improve performance by reordering multiple outstanding requests that are already queued, picking the one needing the least head movement first. In a system that loads and runs a single sequential user process at a time, the process issues only one I/O request at a time and must wait for it to complete before issuing the next — there is never more than one pending request for the scheduler to reorder. Since SSTF and FCFS process a lone request identically, there is no actual queue to optimise, so the real-world improvement for user-program I/O is 0% regardless of what the vendor's synthetic benchmark (presumably run under multiprogramming with many queued requests) claims, option (iv).