There are 200 tracks on a disc platter and the pending requests have come in the order: 36, 69, 167, 76, 42, 51, 126, 12 and 199. Assume the arm is located at the $100^{th}$ track and moving towards track 200. If sequence of disc access is 126, 167, 199, 12, 36, 42, 51, 69 and 76 then which disc access scheduling policy is used?
- A. Elevator
- B. Shortest seek-time first
- C. C-SCAN
- D. First Come First Served
Answer: C. C-SCAN
Explanation: The head moves from 100 towards 200, serving 126, 167, 199. Then it jumps to the beginning (lowest track) without serving, i.e., to 12? Or jumps to end? In C-SCAN it jumps to the other end. Here it goes 199 -> 12 -> 36 ... which indicates a jump to the lowest request and servicing upwards. This circular behavior characterizes C-SCAN.