In SSTF (Shortest Seek Time First), requests having shortest seek time are executed first. So, the seek time of every request is calculated in advance in the queue and then they are scheduled according to their calculated seek time. As a result, the request near the disk arm will get executed first. SSTF is certainly an improvement over FCFS as it decreases the average response time and increases the throughput of system

Characteristics of SSTF :

The request with shortest seek time is executed first hence decreasing the Average Response Time.

Advantages of SSTF :

Average Response Time decreases
Throughput increases

Disadvantages of SSTF :

Overhead to calculate seek time in advance
Can cause Starvation for a request if it has higher seek time as compared to incoming requests
High variance of response time as SSTF favours only some requests