CS 3733 Operating Systems, Fall 2008 Exam 1 Comments

Grade distribution:

• 90-99: 2
• 80-89: 5
• 70-79: 9
• 60-69: 2
• below 60: 4
• Average: 72

• Problem 2a: The possible return values are -1, 1, 2, or 3.
  0 is not a possibility since you have not reached the end of the file.
  The buffer contains 4 bytes and starts with ABCD.
  Some of these may be overwritten, but the buffer will not contain "garbage".
• Problem 2b: There are a large number of possibilities. Either read can return -1, 1, 2 or 3.
  For most of these return values there are many possibilities.
• Problem 3: The reads are independent, but each may still return -1, 1, 2, or 3.
• Problem 4: Several people forgot to say what the operations do.
  A semaphore is not "something used to solve the critical section problem." This is just one of the ways it can be used.
• Problem 5f: All generalizations are false, including this one.
  Sometimes bounded waiting is bad. If one process is a solitaire game and the other controls the temperature in the core of a nuclear reactor, you do not want to delay lowering the temperature of the core to move the black queen on the red king.
  Sometimes busy waiting is a good thing. If you have multiple CPUs, or if you are waiting for an independent device, like a disk controller, it may be more efficient to use busy waiting if you know the wait will always be short.

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