a. New requests for the track over which the head currently residescan theoretically arrive as quickly as these requests are beingserviced.b. All requests older than some predetermined age could be “forced”to the top of the queue, and an associated bit for each could beset to indicate that no new request could be moved ahead ofthese requests. For SSTF, the rest of the queue would have to bereorganized with respect to the last of these “old” requests.c. To prevent unusually long response times.d. Paging and swapping should take priority over user requests. Itmay be desirable for other kernel-initiated I/O, such as the writingof file system metadata, to take precedence over user I/O. If thekernel supports real-time process priorities, the I/O requests ofthose processes should be favored.