Consider a disk queue with requests for I/O to blocks on cylinders 98, 183, 37, 122, 14, 124, 65, 67 in that order. If the disk head is initially at cylinder 53. Using SSTF scheduling, Arrange the following movement of head position in order of transversal. A. 67 B. 37 C. 65 D. 98 E. 14 Choose the correct answer from the options given below:
SSTF Disk Scheduling Explained
The Shortest Seek Time First (SSTF) disk scheduling algorithm serves pending I/O requests by servicing the request with the minimum seek time from the current head position.
Mapping Cylinder Requests
First, map the given letters to their corresponding cylinder numbers:
- A = 67
- B = 37
- C = 65
- D = 98
- E = 14
The initial head position is 53.
SSTF Algorithm Steps
We apply the SSTF logic to determine the order of head movement, focusing on the cylinders mentioned in the options.
Step 1: Initial Movement
Current head position: 53.
Calculate the seek time to each relevant cylinder:
- To C (65): $|65 - 53| = 12$
- To A (67): $|67 - 53| = 14$
- To B (37): $|37 - 53| = 16$
- To E (14): $|14 - 53| = 39$
- To D (98): $|98 - 53| = 45$
The shortest seek time is 12, towards cylinder 65 (C).
Movement Order: C
Step 2: Second Movement
Current head position: 65.
Remaining relevant cylinders: {A, B, D, E}. Calculate seek times:
- To A (67): $|67 - 65| = 2$
- To B (37): $|37 - 65| = 28$
- To D (98): $|98 - 65| = 33$
- To E (14): $|14 - 65| = 51$
The shortest seek time is 2, towards cylinder 67 (A).
Movement Order: C, A
Step 3: Third Movement
Current head position: 67.
Remaining relevant cylinders: {B, D, E}. Calculate seek times:
- To B (37): $|37 - 67| = 30$
- To D (98): $|98 - 67| = 31$
- To E (14): $|14 - 67| = 53$
The shortest seek time is 30, towards cylinder 37 (B).
Movement Order: C, A, B
Step 4: Fourth Movement
Current head position: 37.
Remaining relevant cylinders: {D, E}. Calculate seek times:
- To E (14): $|14 - 37| = 23$
- To D (98): $|98 - 37| = 61$
The shortest seek time is 23, towards cylinder 14 (E).
Movement Order: C, A, B, E
Step 5: Fifth Movement
Current head position: 14.
Remaining relevant cylinder: {D}. Calculate seek time:
- To D (98): $|98 - 14| = 84$
The shortest seek time is 84, towards cylinder 98 (D).
Movement Order: C, A, B, E, D
Final SSTF Order
The complete order of head movement for the specified cylinders using SSTF scheduling is C, A, B, E, D.
Important Questions from Disk Scheduling
Which of the following is the time taken to move an access arm to a certain track on a disk?
Move the Read/Write head of disk in or out to position on a correct track is known as ______.
_______ is a process of lifting the process from memory and placing it on disk.
- Match List I with List II
List I List II A. RAID Level 2 I. Block interleaved distribution parity B. RAID Level 3 II. Also known as P+Q redundancy Scheme C. RAID Level 5 III. Bit interleaved parity D. RAID Level 6 IV. Also known as Memory style error correcting code organization
Choose the correct answer from the options given below: - What shall be the total head movement of cylinders if the FCFS disc scheduling method is used ?
