CS 3733 Operating Systems, Spring 2007 Exam 2 Comments

Grade distribution:

• 90-96: 2
• 80-89: 6
• 70-79: 12
• 60-69: 5
• below 60: 4
• Average: 74
• Median: 74

Comments on individual problems:

1. This one caused the most trouble.
   There is only one process signal mask per process.
   It determines which signals are blocked.
   The three data structures, maskblocked, maskunblocked, and maskold are sets of signals, not signal masks.
   Only lines 5, 7, and 8 change the process signal mask.
   Line 4 changes a data structure, but does not directly affect which signals are blocked.
   Line 6 does not wait for a signal, it initiates a loop which checks a variable.
   Line 7 waits for a signal.
   Line 7 does not suspend a signal, it suspends the process.
2. Since the head has just moved from 24 to 36, it is moving toward larger cylinders when these algorithms start.
   It starts at 36. 40 is closer to 36 than 31 is.
3. There are two possible correct answers for a) since the TLB lookup can be done in parallel or in series with the page table lookup.
   You should be able to do this calculation without a calculator.
   The only multiplications are by 2.
   For b) you need to assume a disk access time.
   Any value which is a few milliseconds is OK.
   Note that 1 in a million is $10^{-6}$ = .000001, not .0000001.
4. This problem does not involve virtual memory so there is no valid bit and no reference bit.
5. This is just like the problem we did in class.