Homework #2 Main memory

Introductory to Operating Systems


Homework #2

Instructions:

1) To complete assignment one, you need to read Chapters 8, and 9 of the textbook.

2) HW must be submitted on typed pdf or word document.  



Q1.(4 points) Assume that the following section of main memory is used to store the page table for 3 different processes. The page-table base register values for process P1 is 1080, for P2 is 1085, and for P3 is 1090. Assume that the contests of memory below correspond to frame numbers. Also assume that frame size is 8192.

 

contents
3
5
7
4
8
2
0
15
11
18
6
20
24
9
10
13
31
38
40
1
Memory addresses
1

0

7

6
1

0

7

7
1

0

7

8
1

0

7

9
1

0

8

0
1

0

8

1
1

0

8

2
1

0

8

3
1

0

8

4
1

0

8

5
1

0

8

6
1

0

8

7
1

0

8

8
1

0

8

9
1

0

9

0
1

0

9

1
1

0

9

2
1

0

9

3
1

0

9

4
1

0

9

5
 

To which physical memory address would the logical address (1, 1200) correspond to if generated by P1?

Answer: _______________

To which physical memory address would the logical address (3, 800) correspond to if generated by P2?

Answer: ______________

Assume that each process has 5 pages. To which process does the following physical address belong and which logical address corresponds to each physical address:

 

Physical address 57344      Process ________Logical address _____________

 

Physical address 57343      Process ____________Logical address _______

Q2. (3 points) A paging system is experiencing a page fault rate of 1 in 1 million page references. When a page fault occurs, 30% of the time an empty frame is not available and frame replacement is needed. Assume that it takes 10 milliseconds to service a page fault needing no frame replacement.  When frame replacement is needed, 40% of time the frame has been modified and it takes 20 milliseconds to service the page fault, in contrast it takes 12 milliseconds when the frame to be replaced has not been modified. It takes 100 nanoseconds to reference a physical memory location and we can neglect the time that it takes to access the page table.

Calculate the effective memory access time for this system under these conditions. Clearly indicate intermediate steps.

Answer:

 

 

 

Q3.(3 points) Consider the following page reference string:

1        2  3  4  2  1  5  6  2  1  2  3  7  6  3  2  6

How many page faults would occur for the following replacement algorithms, assuming three and four frames? Remember that all frames are initially empty, so your first unique pages will cost one fault each.

·         FIFO replacement

·         Optimal replacement

·         LRU replacement