CS414 - Homework 1 Answer Keys

1.  Why are distributed systems desirable?

Distributed systems are desirable for many reasons, which include 

1) increase throughput due to load and job sharing, 
2) provide a higher reliability (graceful degradation/partial operability), 
3) reduce system cost by resource sharing.

2.  What is multiprogramming? What are its advantages over uniprogramming? 
    How is it different from multiprocessing?

Characteristics:

   o multiple programs (processes) exist in memory
   o overlapping I/O time of one job with CPU time of another

Advantages:

   o efficiency due to overlapping

Difference from multiprocessing:

   o multiprocessing means the system uses multiple processors

3.  Difference between "kernel mode" and "user mode" instructions

Kernel mode instructions:

   o only executable in kernel mode
   o instructions having potential to damage system or other users

User mode:

   o usable in both modes
   o not possible to interfere with other user or system

Reason for dual mode: protection of the system.

4.  Which of the following instructions should be privileged?

   a.disable all interrupts - yes
   b.read the time-of-day clock - no
   c.set the time-of-day clock - yes
   d.read the timer - no
   e.set the value of the timer - yes
   f.clear memory - yes
   g.switch from user mode to privileged mode - yes