A good disk scheduling policy can increase the disk access performance. The performance of the following disk scheduling policies: (i) First-in-first-out (FIFO), (ii) Shortest-service-time-first (SSTF), (iii) SCAN, and (iv) circular SCAN (C-SCAN), are analysed. The disk scheduler receives the following track request in the order of 90, 180, 175, 30, 120, 45, 170, 140, 190. Assume that the disk head is initially positioned over track 100 and is moving in the direction of decreasing track number. Copy Table 4 to the answer script and complete the table. (b) A computer server has several disks to store data using RAID technology. If a large file is required to read quickly by the server in a short period of time, which level of RAID do you recommend? Briefly explain your recommendation. (c) What is a disk cache? Briefly explain the advantage of using disk cache