. (4 pts) Write a few sentences to explain in which of the four IO software layers each of the following is done: Computing the track, sector, and head for a disk read Writing commands to the device registers Checking to see if the user is permitted to use the device Converting octal characters into a single binary value 4. (6 pts) Disk requests come into the disk driver for cylinders 40, 10, 20, 22, 42, 8, 2 and 29, in that order. A seek takes 5 msec per cylinder moved. Assuming the disk arm is initially at cylinder 25, compute the total seek time for each of the following: First-come, first-served Closest cylinder next Elevator algorithm, initially moving down (towards lower cylinder end)