1. (4 pts)
   b switch to monitor mode 
   d write into monitor memory
   g turn off time interrupt

   Dispute
   c read minitor memory 
     (Solution manual lists it as one of the answers. The only reason we
      can give is for security. However, system won't go down for that. 
      Therefore, I don't deduct any point from you for it.)
   
   Common error
   e fetch instruction from monitor memory
     (We don't protect it. In fact, we implement system call by that.)

2. (4 pts)
   XYUVW XUYVW XUVYW XUVWY 
   UXYVW UVXYW UVWXY
   UXVYW UXVWY
   UXVWY

3. (8 pts)
   Interleaved 
   (1) CPU utilization=18/21
       I/O utilization=12/21
   (2) throughput=2/21
   (3) turnaround time=(19+21)/2=20

   Sequential
   (1) CPU utilization=18/30
       I/O utilization=12/30
   (2) throughput=2/30
   (3) turnaround time=(15+30)/2=22.5

4. (4 pts)
   <omit>