Reading: Questions

MOS 1.4-1.5

• BIOS (Basic Input/Output System) is typically held in a flash memory. Is it possible to put the BIOS on disk instead? Please tell briefly the pros and cons of on flash memory and on disk.
• The simplest way to bootstrap an operating system is to boot from a binary image on a disk. What would you need to do if you are building a diskless workstation or a network computer which needs to bootstrap from a network file server? Explain your idea of how to do that.

MOS 1.6-1.7

• What is the difference between a system call and a library call?
• What are the advantages and disadvantages of the micro-kernel approach?

MOS 2.1-2.2

• What are the differences between a program and a process?
• What are the differences between a process and a thread?
• Write the psuedo-code to perform a process context switch

MOS 2.2.3-2.3.3

Goal: Understand different kinds of threads as well as the concept of a critical section.

• What are the differences between a kernel thread and a user-level thread?
• Suppose two students share a house and they share the responsibility of buying milk, but their fridge is small. So, they would like to avoid buying too much milk. One day,

  Time	Student A	Student B
  3:00	Looks in fridge. No milk.
  3:05	Bikes to WaWa
  3:10	Arrives at WaWa	Pours cereal. Looks in fridge. No milk.
  3:15	Buys milk	Drives to WaWa
  3:20	Arrives and and puts milk away	Arrives at WaWa
  3:25		Buys milk
  3:30		Arrives at home. Pours milk into cereal, then puts it away in the fridge.

  At each step, the student can be distracted and do other things. How would you solve this problem?

MOS 2.3.3, 2.3.6

• The simplest way to implement Acquire() and Release() is:

  Acquire() { disable interrupts; } Release() { enable interrupts; }

  Do you think it works? If so, under what conditions? If do not think so, explain why it does not work and how would you make it work.
• The textbook mentioned using a test-and-set instruction to implement mutual exclusion. How would you use it to implement Acquire() and Release()?

MOS 2.4 (2e: 2.5)

Goal: Understand the criteria and methods of CPU scheduling

• The non-preemptive scheduler in project 2 uses the First-Come-First-Serve (FCFS) method. Compare this approach with the round-robin scheduling. Under what conditions is the FCFS approach preferred? Under what conditions is round-robin preemptive scheduling approach better?
• Round-robin schedulers normally maintain a list of ready processes or threads without duplicates. What would happen if a process or thread occurs more than once in this list? Is there a case where you would like to do that?

MOS 6 (2e: 3)

Goal: Understand the cause of deadlocks and think about the best solution.

• The textbook lists four conditions for a deadlock (3.2.1) to occur. Discuss what happen if we remove any one of them.
• The textbook also lists four strategies to deal with deadlocks (3.3.2):
  • ignore the problem
  • detect and recover
  • avoid deadlocks by careful resource allocation
  • prevent deadlocks by negating a necessary condition
  Explain which strategy you prefer and how you would implement it.

MOS 5.1-5.3, 5.5-5.9

A complicated issue in designing a device driver is to provide asynchronous operations.

• What design and implementation issues will you need to consider if you want to provide users with asynchronous operations? List the issues you can think of and make some comments on each.

MOS 2.3.8, 8.2.1-8.2.4

• Consider implementing inter-process communication primitives send(destination, msg, n) and recv(source, buffer, max), where destination and source specify the destination process and source process respectively. Provide psuedo-code to show how to implement the two primitives. Your code should consider issues with synchronization and buffer management.

MOS 3.1-3.3.3 (2e: 4.1-4.3.3)

• What virtual memory related states do you need to keep in a PCB?
• What virtual memory related tasks does an OS kernel need to do during a context switch?

MOS 3.4 (2e: 4.4)

The textbook describes 10 page replacement algorithms in Section 4.4.

• Which two algorithms do you like the best? Explain why.
• What minimal hardware mechanisms do your favorite algorithms need?

MOS 3.5-3.6 (2e: 4.6-4.7)

• How do you avoid virtual memory thrashing?
• When a process forks off a child process, it needs to replicate its address space. This operation may take a while to complete. One technique to speed this up is to create an address space mapping to the same set of pages without copying data and mark all pages read-only. On a write, the kernel will catch the access fault, allocates a page frame, copy the page from its parent process, mark the page to be read-write, and then return to the faulting instruction. This technique is called "copy-on-write." How would you implement copy-on-write?

MOS 5.4

• The textbook describes two disk arm scheduling algorithms (SSF and Elevator). Discuss which you prefer and why?
• The textbook mentions RAID. What are the advantages and disadvantages of level 4 and level 5?

MOS 4.1, 9.3.1-9.3.3 (2e: 6.1, 9.6)

• If you are in charge of designing a file system API, what issues must you consider? List a number of issues and explain, using a sentence for each, why it must be considered.
• The textbook mentioned three protection mechanisms in Section 9.6. Could you apply them to file systems? Please state your opinion and briefly provide your supporting arguments.

MOS 4.2-4.3.3, 4.5.2-4.5.3 (2e: 6.2-6.3.3, 6.4.3, 6.4.5)

• The textbook lists three ways to implement files: linked list allocation scheme, linked list allocation with an index, and i-node. What is your favorite scheme and why.
• What is your favorite method to implement file directories? Discuss why you like your choice.

MOS 4.4.2-4.4.4, 4.3.5 (2e: 6.3.6-6.3.8)

• State very briefly what to do in order to make a log-structured file system be consistent after a crash.
• What is the difference between a file buffer cache and virtual memory?