CS560 Final Exam - May 4, 2005

Jim Plank

Question 1 (8-12 points)

• How are files organized?
• What metadata is needed for the operating system to find the bytes of a file?
• How are the blocks on the disk organized and maintained?
• Discuss caching in such a system -- what kinds of caching would be beneficial?

Question 2 (10-12 points)

• Pointers are four bytes.
• Pages are 8K.
• There are four segments.
• Each segment is represented by two registers - a segment table base register (STBR) and a segment table length register(STLR). These point to the single-level page tables for each segment.
• Each PTE takes 4 bytes, and is composed of a 27-bit pointer, plus five bits: used, dirty, read, write, execute.

Answer the following questions:

• A: How many pages can there possibly be in a segment (do not include the page table as part of this -- just the memory in the segments)? You may express your answer as a power of two.

• B: How many pages can there possibly be in a segment's page table? Again, you may express your answer as a power of two. (In this question, I mean how many pages compose the memory used by the segment's page table, not the number of PTE's).

• C: Suppose a program is executing, and at a certain point in time, it has the following sizes of its memory regions:
  • Code: 200K
  • Globals: 24K
  • Heap: 8M
  • Stack: 64K

  Suppose page 0 of virtual memory is invalid. Moreover, suppose each of these regions is stored in a different segment. Show how the virtual address space of the program is partitioned. (e.g. something like "addresses 0 to 54ff are invalid; addresses 0x5500 to 0x5fff correspond to the XX segment; addresses 0x6000 to 0x10fff are invalid, etc.")

• D: Given the scenario for C above, how many pages of memory will be used to store the process's page tables?

Question 3 (7-10 points)

       char *gets(char *s);

       gets() reads a line from stdin into the buffer pointed to  by  s  until
       either  a  terminating newline or EOF, which it replaces with the
       NULL character (0). 

Question 4 (4-7 points)

Question 5 (15 - 20 points)

Here is a piece of code that does matrix multiplication on two square matrices. A matrix with n rows and n columns is represented by an array a, which has n*n elements. The element in the i-th row and the j-th column is in a[i*n+j] (obviously, we are using standard zero-indexing). Mmult() multiplies matrices a and b and puts the result into c:

mmult(double *a, double *b, double *c, int n)
{
  int i, j, k;

  for (i = 0; i < n; i++) {                 /* Loop 1 */
    for (j = 0; j < n; j++) {               /* Loop 2 */
      c[i*n+j] = 0;
      for (k = 0; k < n; k++) {             /* Loop 3 */
        c[i*n+j] += (a[i*n+k] * b[k*n+j]);
      }
    }
  }
}

Part 1

Part 2

Part 3

Part 4

Part 5