What do you mean by an Operating System? What are the three main purposes of an operating system? Write a short note on, "An operating system is a resource allocator".

List five services provided by an operating system and explain how each creates convenience for users.

Give two reasons why caches are useful. What problems do they solve? What problems do they cause? If a cache can be made as large as the device for which it is caching (for instance, a cache as large as a disk), why not make it that large and eliminate the device?

Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU's execution load.
i) How does the CPU interface with the device to coordinate the transfer?

ii) The CPU is allowed to execute other programs while the DMA controller is transferring data. Does this process interfere with the execution of the user programs? If so, describe what forms of interference are caused.

Describe the differences among short-term, medium-term, and long-term scheduling.

What do you know about process and process control block (PCB)? What are the states of process? Explain with necessary diagrams.

What are two differences between user-level threads and kernel-level threads? Under what circumstances is one type better than the other?.

What are the benefits and the disadvantages of synchronous and asynchronous communication? Consider both the system level and the programmer level.

Explain the difference between preemptive and non-preemptive scheduling.

A multithreaded web server wishes to keep track of the number of requests it services (known as hits). Consider the two following strategies to prevent a race condition on the variable hits.

Explain which of these two strategies is more efficient.

What advantage is there in having different time-quantum sizes at different levels of a multilevel queueing system? Explain with example.

Regarding the Producer-Consumer problem, explain the following term:
i) Producer process   ii) Consumer Process   iii) Unbounded-buffer   iv) Bounded-buffer

The following processes are being scheduled using a Priority Scheduling-Preemptive algorithm. Each process is assigned a numerical priority, with a higher number indicating a higher relative priority.

i) Show the scheduling order of the processes using a Gantt chart.
ii) Fill the following table for exit time, turn-around time, and waiting time:

Suppose that a system is in an unsafe state. Show that it is possible for the processes to complete their execution without entering a deadlocked state.

Consider the following snapshot of a system:

Answer the following questions using the banker's algorithm:

i) What is the content of the matrix Need?

ii) Define safe and unsafe state. Is the system in a safe state? If so, show a safe order in which the processes can execute.

iii) If a request from process P1 arrives for (0,4,2,0), can the request be granted immediately?

List two deadlock detection mechanisms. Construct the wait-for graph that corresponds to the following resource allocation graph and determine whether or not there is deadlock.

In a system with a TLB, assume the following:

i) the memory access time is 150 nsec.     ii) the TLB access time is 25 nsec.

iii) the TLB hit rate is 80%.

Compute the effective access time for memory in this scenario.

Given memory partition of 100 KB, 500 KB, 200 KB and 600 KB (in order), how would each of the first fit, best fit and worst fit algorithms place processes of 212 KB,417 KB,112 KB and 426 KB (in order)? Rank the algorithms in terms of how efficiently they use memory.

What is paging? Consider a logical address space of 64 pages of 1,024 words each, mapped onto a physical memory of 32 frames.

i) How many bits are there in the logical address?

ii) How many bits are there in the physical address?

Explain the difference between internal and external fragmentation.

Define virtual memory. How does it empower computing?

What does TLB stands for? Briefly explain its usage in operating system.

What is fragmentation? Consider the following segment table:

What are the physical addresses for the following logical addresses?

i) 0, 430   ii) 1, 10   iii) 2, 500   iv) 3, 400

Consider the following page reference string:

2, 3, 2, 1, 5, 2, 4, 5, 3, 2, 5, 2

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

i) Least Recently Used (LRU)

ii) Optimal Page Replacement

iii) FIFO

Suppose that a disk drive has 200 cylinders, numbered 0 to 199. The drive is currently serving a request at cylinder 50. The queue of pending requests, in FIFO order, is:

      95, 180, 34, 119, 11, 123, 62, 64

Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests? You should also provide a graphical view of head movement for each of the following disk-scheduling algorithms.

i) C-SCAN

ii) LOOK

Define following terms:

i) Thrashing

ii) RAID