This exam is open-book, open-notes, open-computer, open-Internet, but closed-other-people. You may, however, ask Jeff Ondich questions.

I know they're not all equally easy, but each question is worth 6 points anyway.

Explain your answers, but do so briefly.

1. List a few events that would cause an operating system's scheduler to get called.
   
   
2. Processes can be scheduled based on a strict priority system. That is, when each process is launched, it is assigned an integer priority, and when the scheduler is called for any reason, it runs the unblocked process whose priority is highest (choosing randomly if there is more than one highest-priority process).

   What are the problems with such a scheduling system? Briefly describe modifications to strict priority that would address these problems.
   
   

3. Consider Peterson's solution to the mutual exclusion problem, as shown in Figure 2-8 on page 37 of Tanenbaum. Suppose you try to modify it to handle three processes by changing N to 3, and changing enter_region to look like this:

   
   void enter_region( int process )
   {
   	int other1 = (process+1) % 3;
   	int other2 = (process+2) % 3;
   	interested[process] = TRUE;
   	turn = process;
   	while( turn == process  &&  (interested[other1] == TRUE || interested[other2] == TRUE) )
   	{
   	}
   }
   

   Using processes numbered 0, 1, and 2, describe a sequence of events that would cause a race condition with this version of enter_region.
   
   

4. Suppose we are using a 2-level page table system in which each second-level page table takes up exactly one page, and we have a 32-bit virtual address space with 4KB pages and 4 bytes per page table entry.
   
   
   • How many bytes will each program need to use to store the first-level page table?
   • Assuming that exactly one second-level page table is in memory and exactly half of its entries are valid, how many bytes of memory in our virtual address space actually reside in physical memory?
   • Why must the first-level page table always be in memory? What would happen if it weren't?
   
   
   
5. What is spooling, and for what is it commonly used? Where does the word "spool" come from?
   
   
6. The UNIX System V-based file system for Linux uses i-nodes that contain 10 direct block pointers, 1 single-indirect block pointer, 1 double-indirect block pointer, and 1 triple-indirect block pointer. If each block is big enough to hold 1024 32-bit block pointers, what is the maximum file size?
   
   
7. Create a UNIX file A. Then create a hard link B to A (using a "ln A B"), create a soft link C to A ("ln -s A C"), and finally delete A ("rm A"). Now execute "cat B" and "cat C". What happens in each case, and why?
   
   
8. Do problem 9 from Chapter 5 of Tanenbaum.
   
   
9. Do problem 13 from Chapter 6 of Tanenbaum.