CS604 Final Term Past Paper Spring 2005

Final Term Examination – Spring 2005

Time Allowed: 90 Minutes

1. This examination is closed book, closed notes, closed neighbors.

Q2. Answer all questions.

1. There is no choice.
2. You will have to answer all questions correctly in this examination to get the maximum possible marks.

Q4. Examination also consists of multiple-choice questions. Choose only one choice as your answer.

1. If you believe that two (or more) of the choices are the correct ones for a particular question, choose the best one.
2. On the other hand, if you believe that all of the choices provided for a particular question are the wrong ones, select the one that appears to you as being the least wrong.

5. All Programming questions should be answered using C syntax. Syntax errors

will not be considered as errors. So try to only answer the question and put your idea and concept using C. Don't use any tool or IDE.

Total Questions: 12

Q1. Marks : 04

Assume that we have a demand-paged memory. The page table is held in CPU registers. It takes 8 milliseconds to service a page fault if an empty frame is available or if the replaced page is not modified and 20 milliseconds if the replaced page is modified. Memory access time is 100 nanoseconds. Assume that the page to be replaced is modified 70% of the time. What is the maximum acceptable page-fault rate for an effective access time of no more than 200 nanoseconds. Show your work.

Q2. Marks : 25

Answer the following questions:

a. (4 Points) Write down names of two process related and two file related system calls in UNIX/Linux.

b. (2 Points) What does the following region statement mean?

region buffer when (count < n) do S1;

c. (4 Point) Consider three cooperating processes P1, P2, and P3. Write the code structures for the three processes using semaphores, insuring that statement S1 in P1 is not executed before statement S2 in P2, and S2 in P2 is not executed before S3 in P3. Show all your work, including initial values for the semaphores used in your code.

d. (2 Point) A system uses a CPU with a memory-to-memory move instruction whose operands may have up to two levels of indirection for both operands. What is the minimum number of frames that a well-behaved process must have in this system to guarantee its successful execution? Why? Assume that the system has 512 MB RAM, 100 GB hard disk, 4 KB pages, and 16-bit memory operands. Show your work.

e. (5 Point) List five basic operating system components.

f. (2 Point) Consider a UNIX-based system that uses a block size of 4 KB. If block addresses take 8 bytes, calculate the total pointer overhead for the biggest possible file on this system. An expression would suffice. What is the size (in bytes) of the largest file that can be stored on this system? Assume that the file inode contains 10 pointers to file blocks. Show all your work.

g. (1 Point) What is the purpose of exponential averaging technique?

h. (1 Point) What is process address space?

i. (1 Point) Name standard files in UNIX/Linux.

j. (3 Points) What is the purpose of medium-term scheduler? Give two reasons for its invocation (i.e., for it to be executed by the OS kernel).

Q3. Marks : 06

Consider a file currently consisting of 100 blocks. Assume that the PCB, bit vector block, index block (in case of indexed allocation), and directory block are in the main memory. Calculate the number of I/O operations required to add a new block in the middle of the file for contiguous, linked, and indexed allocation techniques. For contiguous allocation, assume that there is no room to grow in the beginning or end of file. Also assume that block information to be added is in a kernel buffer. Show your work.

Contiguous Allocation: · Linked Allocation: · Indexed Allocation:

Q4. Marks : 05

Consider a pure demand paging system with a paging disk that has an average access and transfer time of 20 milliseconds. Addresses are translated through a page table in main memory, with an access time of 50 nanoseconds per memory access. Thus, each memory reference through the page table takes two accesses. To improve this time, we have added cache memory that reduces access time to one memory reference, if page table entry is in the cache. Assume that cache access time is negligible. Assume that 80% of the accesses are in the cache, of the remaining, 10% cause page faults, and 50% of the replaced pages are dirty. Write down the expression / equation for the effective memory access time for the computer system. Show your work.

Q5. Marks : 20

Consider a computer system with the following specifications and answer the questions that follow. The system uses a cache (TLB) to contain part of the page table for a process. Show your work.