Test 3
Operating Systems and Networking
CS330
Fall 2012
Exam date: November 20, 2012
Exam modality: No books, no notes, no laptops, and no cellphones
Answer three questions from Group A and two questions from Group B
Group A. Answer three questions from this group.
1. What is garbage collection? Why is it necessary? Under what condition(s), garbage collection
in real memory becomes an inefficient process? Suggest a way to handle the garbage collection
problem that would avoid such situations.
2. One depressed Operating System designer claims that it really does not matter what storage
placement strategy (like Best Fit, First Fit, etc.) is used. Sooner or later a system achieves steady
state, and all of the strategies known to mankind since the early days of Ramses II perform
similarly. Do you share her unbounded optimism? Explain.
3. Placement strategies determine where in the main storage incoming programs and data should
be loaded. Suppose a job waiting to begin execution has a storage requirement that can be
fulfilled immediately. Should the job be loaded and begin execution immediately? Explain.
4. (a) A process is seemingly generating a large number of page faults. Argue both for and against
giving the process high priority for the CPU. (b) Suppose you put a tap on an I/O channel and
observe heavy page traffic. Does this imply thrashing? Explain.
5. For a virtual memory system employed via paging, the address space is 32-bits long. Assume
page size to be 8192 bytes. What is the maximum number of pages a process could possibly
have? Instead of using a standard page table per process, it has been decided to use hashing to
convert page number into a frame number. Suggest how it could be approached. How would you
handle collision in such a scheme?
6. Suppose a process with a reference string Z = a b c d a b e a b c d e b a b c d e is allocated three
frames under FIFO scheme. How many page faults does it suffer? What happens when the
allocated number of frames is 4, instead? Explain the results.
Group B. Answer any two questions from this group
7. What are the advantages of layered protocols? List at least two disadvantages they commonly
are endowed with.
8. In what significant ways LAN networks are different from non-LAN networks? A LAN
network could be entirely wired, or mixed. For a single mixed LAN unit, do you envisage any
operational constraint? If so, discuss them.
9. A host H1 wants to communicate with a host H 2 using a point to point transmission over a
cable of length L and bandwidth (the channel capacity) of 10 Mb/s. She wants to figure out her
transmission time to transmit a file of size F bytes. However, she has forgotten the necessary
formula, and she has to reason it out. She correctly realizes that both F and B are involved in
transmission time Tr computation. What would be the transmission time in her case if
F  20KB .
Similarly, she is interested in computing the propagation time. If the speed of light is
c  2 108 m / s , and the distance to H 2 is 4000 Km from the station, what is the propagation
time? How long would it take for her to send two files to her friend if she needs exactly one ACK
bit (for acknowledgment) from her friend?
10. You are given a network address of 197. 13. 0. 0 and a subnet mask of 255.255.0.0. Your
manager has asked you to create 4 sub networks with the capability of one hosting 8000 devices,
and the other three with 4000 hosts on each of them. List all subnets along with their subnet
masks, and IP address range for each sub-network.