Consider the following five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time. (P, 155), (Q, 85), (R, 110), (S, 30), (T, 115) Assume the head is positioned at cylinder 100. The scheduler follows Shortest Seek Time First scheduling to service the requests. Which one of the following statements is FALSE?

Initial head position: 100 Pending requests: P (155), Q (85), R (110), S (30), T (115)

Using Shortest Seek Time First (SSTF) scheduling, the scheduler always services the request closest to the current head position:

1. From 100:

   • Distance to P(155): $|100-155| = 55$

   • Distance to Q(85): $|100-85| = 15$

   • Distance to R(110): $|100-110| = 10$ (Minimum)

   • Distance to S(30): $|100-30| = 70$

   • Distance to T(115): $|100-115| = 15$

   • Service R (110).

2. From 110:

   • Distance to T(115): $|110-115| = 5$ (Minimum)

   • Distance to Q(85): $|110-85| = 25$

   • Distance to P(155): $|110-155| = 45$

   • Distance to S(30): $|110-30| = 80$

   • Service T (115).

3. From 115:

   • Distance to Q(85): $|115-85| = 30$ (Minimum)

   • Distance to P(155): $|115-155| = 40$

   • Distance to S(30): $|115-30| = 85$

   • Service Q (85).

4. From 85:

   • Distance to S(30): $|85-30| = 55$ (Minimum)

   • Distance to P(155): $|85-155| = 70$

   • Service S (30).

5. From 30:

   • Service P (155).

Sequence of servicing: $R \rightarrow T \rightarrow Q \rightarrow S \rightarrow P$.

• Statement in (A): "T is serviced before P" is TRUE.

• The statement in option (B) from the exam is "Q is serviced after S, but before T", which is FALSE because Q is serviced *before* S and *after* T.

Hence, option (B) is the false statement.