SSTF Full Form

What Is The Full Form Of SSTF?

The full form of SSTF is Shortest Seek Time First.

SSTF is a secondary storage scheduling algorithm that determines the motion of the disk’s head and arm in servicing the read and write requests. SSTF acts as a disk scheduling algorithm, and it is an improvement upon the FCFS algorithm. It selects the requests with the least seek time starting from the current head position. Scheduling priority goes to the processes with the shortest seek- even if the requests aren’t the first ones in the queue.

SSTF implements this by calculating the seek time of every request in the queue in advance. It then schedules the requests according to their seek time. However, this process doesn’t ensure fairness and can lead to unspecified postponement. The seek pattern is highly localized in SSTF, and it is like SJF (Shortest Job First) because it can prevent distant requests from being serviced under heavy load. This phenomenon is known as Starvation.

Characteristics of SSTF

• SSTF is an algorithm that stands for Shortest Seek Time First.
• The algorithm selects the requests with the minimum seek time- from the current head position.
• Since the seek time increases with the total number of cylinders traversed by the head, the SSTF algorithm chooses the pending request that is closest to the current head position.
• The algorithm seems reasonable. It services all the requests that are close to the current head position before it moves the head far away to service other requests. This assumption is the basis for the SSTF (shortest-seek-time-first) algorithm.
• As compared to FCFS, the total seek time is low.
• SSTF breaks the tie in the direction of the head movement.
• The aim of SSTF is to provide increased throughput.
• The SSTF algorithm services those requests that require the least number of head movements from the current position- irrespective of the direction.
• The waiting time is less in SSTF.
• The average response time is low because of the algorithm.
• SSTF may not act as a fair algorithm towards the sequence of project requests.

Benefits of SSTF

• The throughput of SSTF is better than that of FCFS.
• The average response time is very low due to the fewer head movements.
• SSTF successfully breaks the tie in the direction of head movement.
• The seek time in SSTF is very much reduced compared to FCFS.
• Waiting time is low.
• Priority of requests has nothing to do with their sequence.

Limitations of SSTF

• Overhead is high because SSTF calculates the seek time of every request in advance.
• Finding the closest request causes the overhead.
• It causes starvation of a request if it has a higher seek time.
• Requests with a lower seek time in a queue get a higher priority even if they didn’t arrive first- making the algorithm unfair.
• The requests that are very far from the head always starve for the CPU.
• Response time and waiting time are highly varied.
• Switching of the direction of the head frequently causes a slowing down of the algorithm.

Keep learning and stay tuned to get the latest updates on GATE Exam along with Eligibility Criteria, GATE Syllabus, Cut off, GATE Previous Year Question Papers, and more.