7. Assume there are four frames in main memory. Consider the following page reference string: 2, 1, 6, 4, 1, 2, 5, 3, 1, 2, 1, 6, 7, 3, 6, 1, 2, 1, 6, 3. How many page faults occur for the OPT (Optimal Page-replacement Algorithm) replacement? Notes: All frames are initially empty, so the first unique pages will all cost one fault.
(A) 7
(B) 8
(C) 9
(D) 10
(E) 11

3. Let x=00001111 and y=11111011 be two 8-bit 2’s complement binary numbers. What happens for x + y? (A) The result is -12 in decimal representation. (B) The result is 12 in decimal representation. (C) The result is -10 in decimal representation. (D) The result is 10 in decimal representation. (E) Overflow occurs.

4. What is bootstrap? (A) an I/O device (B) a memory device (C) an interrupt handler (D) a processor (E) a small initiation program to start up computers

5. CPU scheduler selects the next process for execution. There are several basic scheduling methods, such as first-in-first-out (FIFO), shortest job first (SJF), and round-robin (RR). Regarding to these methods, which of the following comments is INCORRECT? (A) With FIFO, the waiting time of a process may depend on the arriving order of the processes. (B) Starvation won’t occur with FIFO. (C) Theoretically, SJF is an optimal scheduling algorithm in terms of average waiting time. (D) Starvation won’t occur with SJF. (E) RR is a preemptive scheduling algorithm.

6. Virtual Memory is a storage allocation scheme in which secondary memory can be addressed as though it were part of main memory. Virtual memory can be implemented using Demand Paging. Several steps are performed in the demand paging scheme: Step 1: Operating system (OS) puts the process in the blocking state. Step 2: CPU is notified and the interrupted process is put in the ready state. Step 3: The required page is brought into the memory with the page replacement algorithm. Step 4: CPU generates an interrupt, indicating a page fault. Step 5: Page table is updated accordingly. Which of the following is the CORRECT sequence of steps performed by demand paging? (A) 1, 2, 3, 4, 5 (B) 2, 4, 3, 1, 5 (C) 3, 2, 5, 1, 4 (D) 4, 1, 3, 5, 2 (E) 5, 3, 1, 2, 4

8. Consider the execution of the following set of processes on a single-core processor.Assume we use preemptive SJF (Shortest-Job-First) scheduling. What is the average waiting time? (A) 10 (B) 12 (C) 14 (D) 16 (E) 18

9. Suppose computers A and B have IP addresses 10.105.1.113 and 10.105.1.91, respectively, and they both use the same netmask N. Which of the values of N given below should be used if A and B belong to the same network? (A) 255.255.255.255 (B) 255.255.255.250 (C) 255.255.255.240 (D) 255.255.255.224 (E) 255.255.255.192

10. Assume a network device sends out data at the rate of 4,000 bps. How long does it cost to send a file of 100,000 characters? (A) 100 seconds (B) 200 seconds (C) 300 seconds (D) 400 seconds (E) 50 seconds

11. The following code snippets have security flaws. Which of the choices below can be used as id to achieve the SQL Injection attack? (A) (B) (C) (D) (E)

12. Suppose we have two tables, named TABLE-A and TABLE-B, respectively, as shown below.  (A) The result is a table of 7 records. (B) There are 5 columns in the resulting table. (C) Green appears in three records of the resulting table. (D) Eight appears in two records of the resulting table. (E) JOIN cannot be performed for these two tables.

13. In a 3-level memory hierarchy system, the hit time for each level is T1 = 5 ns (L1-cache) T2 = 200 ns (L2-cache) T3 = 600 ns (Main memory) The local hit rate in each level is H1 = 0.9 (L1-cache), H2 = 0.8 (L2-cache), and H3 = 1 (It is assumed that we can always find the data in main memory). If the average access time (ns) of this memory is K. What is the value of “{Round(K*123)} mod 5” ? (A) 0 (B) 1 (C) 2 (D) 3 (E) 4