3. Using the information given, calculate I/O access speed using CPU 1 each    of the four disk drives as they evaluate the following track request: 0, 31, 20, and 15,20,31,15. In each case, determine whether reordering the request would be advantageous.

CPU               TIME FOR 1000 INSTRUCTIONS
1                              30.0 ms
2                              1.2 ms
3                              0.2 ms

DISK DRIVE                    ACCESS SPEED
   A                              35 ms
   B                              10 ms
   C                              5 ms
   D                               50 ms


4. Describe how you would us a negative feedback loop to avoid eating too much food during each course of a very large meal.
Calculate the availability of a server with an MTBF of 80 hours and a MTTR of 3 days (72 hours).