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Department of Computer Science, UMass Amherst Andrew H. Fagg

Final Exam

Final Exam covers:

˛ 50% of the exam is on the recent material (segmented paging, virtual

memory, page replacement, I/O systems and distributed ¯le systems).

˛ 50% of the exam is comprehensive (mostly material covered in exams 1

and 2).

The exam is closed book, closed electronic device, closed notes. Except {

you are allowed 1 sheet of paper for notes.

CMPSCI 377: Operating Systems Lecture 26, Page 1

Department of Computer Science, UMass Amherst Andrew H. Fagg

General Skills

˛ You should have a good sense of how the pieces ¯t together and how

changes in one part of the OS might impact another.

˛ You will not be asked detailed questions about any speci¯c operating

system such as Unix, Windows NT.

CMPSCI 377: Operating Systems Lecture 26, Page 2

Department of Computer Science, UMass Amherst Andrew H. Fagg

Memory Management

1. What is virtual memory and why do we use it?

2. What is paging? what is the diŽerence between a page and a frame?

3. What does the OS store in the page table?

4. What is a TLB? How is one used?

5. What is Segmentation? Why is it useful?

6. How do we get the best of both worlds? Segmented paging. How does it

work?

) Make sure you understand how to translate between virtual and physical

addresses.

CMPSCI 377: Operating Systems Lecture 26, Page 3

Department of Computer Science, UMass Amherst Andrew H. Fagg

Memory Management: Virtual Memory

1. Why does virtual memory work?

2. What is a page fault, how does the OS know it when a page has faulted,

and what does the OS do when a page fault occurs?

3. Page replacement algorithms: FIFO, MIN, LRU, Second chance. For

each: understand how they work, and their advantages and disadvantages.

CMPSCI 377: Operating Systems Lecture 26, Page 4

Department of Computer Science, UMass Amherst Andrew H. Fagg

I/O Management

1. How does the OS communicate with I/O devices?

Polling vs interrupts vs DMA

2. What are I/O buŽers used for?

3. What are I/O caches used for? How do they aŽect reading and writing to

I/O devices?

4. What are the primary delays in accessing a disk? How do we improve this

access time?

5. Disk scheduling algorithms: FIFO, SSTF, SCAN, C-SCAN. How do they

work, advantages and disadvantages.

6. What I/O abstractions are implemented by the OS?

CMPSCI 377: Operating Systems Lecture 26, Page 5

Department of Computer Science, UMass Amherst Andrew H. Fagg

Distributed ¯le systems

(we will touch on this material today)

1. What are location transparent names?

2. What are location independent names?

3. What does it mean to say that a distributed ¯le system has a single

(global) namespace?

4. What is a cache?

5. What are the advantages of using a cache in a distributed ¯le system?

What are the disadvantages?

6. What are the advantages and disadvantages of write-back and

write-through caches?

CMPSCI 377: Operating Systems Lecture 26, Page 6