SSTF (Shortest Seek Time First) in Operating Systems - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does SSTF stand for in disk scheduling?

SSTF stands for Shortest Seek Time First. It is a disk scheduling algorithm that selects the disk I/O request closest to the current head position to minimize seek time.

beginner

How does SSTF decide which disk request to serve next?

SSTF chooses the request that requires the least movement of the disk arm from its current position, reducing the seek time for each operation.

intermediate

What is a potential drawback of the SSTF algorithm?

SSTF can cause starvation, where some requests far from the current head position may wait a long time if closer requests keep arriving.

intermediate

Compare SSTF with FCFS (First-Come, First-Served) in disk scheduling.

SSTF usually reduces average seek time by choosing the closest request next, while FCFS serves requests in arrival order without considering distance, which can lead to longer seek times.

advanced

In what scenario might SSTF perform poorly despite its goal to minimize seek time?

If requests are clustered far apart, SSTF might keep switching between nearby requests and neglect others, causing some requests to wait too long, leading to starvation.

What is the main goal of the SSTF disk scheduling algorithm?

A Serve requests from the outer edge to the inner edge

B Serve requests in the order they arrive

C Minimize the seek time by selecting the closest request

D Serve requests randomly

SSTF selects the disk request closest to the current head position to reduce seek time.

Which problem can SSTF cause when handling disk requests?

A Starvation of some requests

B Increased total seek time always

C Ignoring the closest requests

D Serving requests in random order

SSTF can cause starvation because requests far from the current head position may wait too long.

How does SSTF differ from FCFS in disk scheduling?

A Both serve requests in the same order

B SSTF serves the closest request; FCFS serves in arrival order

C SSTF serves requests randomly; FCFS serves closest first

D FCFS minimizes seek time; SSTF does not

SSTF picks the closest request to minimize seek time, while FCFS serves requests as they arrive.

If the disk head is at position 50, and requests are at 45, 55, and 60, which will SSTF serve next?

A Request at 50

B Request at 55

C Request at 60

D Request at 45

Requests at 45 and 55 are both 5 units away from 50, so SSTF can choose either. Typically, it picks the closest; if equal, either can be chosen.

Which of these is NOT a characteristic of SSTF?

A Always serves requests in arrival order

B Minimizes seek time

C Can cause starvation

D Selects the nearest request to current head

SSTF does not serve requests in arrival order; it serves the closest request next.

Explain how the SSTF disk scheduling algorithm works and one advantage and one disadvantage of using it.

Think about how the disk arm moves and what happens to far away requests.

Compare SSTF with FCFS disk scheduling in terms of seek time and fairness.

Consider both efficiency and how requests are treated over time.