• University of Massachusetts, Amherst

• COMPSCI 230

COMPSCI 230 Computer Systems Principles B

Final Exam

ANSWER SHEET FOR PROGRAMMING QUESTION

1. 100001101 or 0110011 2. d

3. sem_wait: line 17 and 27 (or 28)

sem_post: line 25 and 30

4. a, c, d

5. 0, 2, 3, 5, 7 6. b, c, e

7.

a b c d e

T N P B T

8. 4

9. b 10. A’s: 4, B’s: 2

11. a, b 12. 454545

13. 7 14. c

15.

a b c d e f

S S C B S B

1

COMPSCI 230 Computer Systems Principles B

Questions:

1. Let N=16, M=64 and P=8, where N is the number of virtual addresses, M is the

number of physical addresses in main memory, and P is the page size in bytes.

Given the table below, what is the physical address, written in binary, that

corresponds to virtual address 0x5?

Valid bit PPN

3 Pts

2. Which of the following(s) about virtual memory address transition is not true?

a. Page tables may be used to map virtual memory addresses to physical

addresses in the RAM

b. Memory management unit (MMU) implements address translation for virtual

memory.

c. Page tables may be used to map virtual memory addresses to physical

addresses in the Disk.

d. When an entry in a page table has its valid bit set to "valid" (1), the "address"

field of that entry may refer to an address on Disk.

2 Pts

2

COMPSCI 230 Computer Systems Principles B

3. Here is a fragment of code shared between N threads:

1. #include <semaphore.h>

2. sem_t s;

3. sem_init(&s, 0, 1);

......

17.

18. printf(“Before I start, the bucket is %i.\n”, bucket_size);

19.

20. while (bucket_size > 0) {

21.

22. printf(“I am filling the bucket with 1 cup and the bucket is %i.\n”,

bucket_size);

23.

24. bucket_size--;

25.

26. sleep(10);

27.

28.

29. }

30.

......

This code is simulating filling a bucket of water 1 cup at a time. The more bucket

fillers we have the better. The problem is that we can only have 1 bucket filler fill the

bucket at a time without a fight (not much room in the bucket filling area!).

Indicates the line number(s) where sem_wait and sem_post should be inserted so

as to ensure correct output and also allow multiple bucket fillers to fill the bucket

without being delayed by other processes' sleep. Noticed that sem_wait and

sem_post cannot be inserted on the same line. No partial credit.