C-LOOK Disk Scheduling Explained

This solution explains the C-LOOK (Circular LOOK) disk scheduling algorithm, specifically the 'Right' direction, for a given set of I/O requests and an initial head position.

Understanding C-LOOK (Right)

C-LOOK is an efficient disk scheduling algorithm. It's similar to SCAN but operates circularly. Here's how C-LOOK (Right) works:

• The disk head starts at a specific cylinder (58 in this case).
• It moves in one direction (Right, towards higher cylinder numbers) servicing all requests in that direction until it reaches the last request in the queue.
• Instead of potentially continuing to the end of the disk and coming back, C-LOOK immediately reverses direction and jumps to the first request in the opposite direction (the lowest numbered request).
• It then services requests in this new direction until all requests are completed.

Analyzing the Request Queue and Head Position

The given parameters are:

• Request Queue: {45, 81, 185, 33, 175, 99, 150, 77}
• Initial Head Position: 58
• Scheduling Algorithm: C-LOOK (Right)

Step-by-Step Processing with C-LOOK (Right)

Let's trace the head movement:

1. Start: The head is at cylinder 58.
2. Direction: The algorithm moves Right (towards higher cylinder numbers).
3. Finding First Request: The requests located at cylinders greater than 58 are {77, 81, 99, 150, 175, 185}. The first request encountered moving right is 77. The head moves from 58 to 77.
   • Movement: 58 to 77
   • Request Processed: 77
4. Finding Second Request: Continuing in the Right direction, the next closest request is 81. The head moves from 77 to 81.
   • Movement: 77 to 81
   • Request Processed: 81
   This is the 2nd request processed.
5. Continuing Right Sweep: The head continues servicing requests in ascending order towards the highest cylinder number:
   • Movement: 81 to 99 (Request Processed: 99)
   • Movement: 99 to 150 (Request Processed: 150)
   • Movement: 150 to 175 (Request Processed: 175)
   • Movement: 175 to 185 (Request Processed: 185)
   The head has now reached the highest request number (185) in this direction.
6. Circular Jump: As per C-LOOK, the head immediately reverses direction and jumps to the lowest request number in the entire queue, which is 33.
   • Movement: 185 (jump) to 33
   • Request Processed: 33
7. Left Sweep: The head now moves in the Left direction, servicing the remaining requests (those smaller than 185 that weren't serviced) in ascending order (from the lowest):
   • Movement: 33 to 45 (Request Processed: 45)
   All requests are now completed.

Processing Sequence Summary

The complete sequence of serviced requests using C-LOOK (Right) is:

Conclusion on 2nd Request

Based on the step-by-step execution of the C-LOOK (Right) algorithm for the given request queue and starting head position, the first request serviced is 77, and the second request processed is 81.