Q. Consider a typical disk that rotates at 15000 rotations per minute (RPM) and has a transfer rate of 50 × 106 bytes/sec. If the average seek time of the disk is twice the average rotational delay and the controller’s transfer time is 10 times the disk transfer time, the average time (in milliseconds) to read or write a 512 byte sector of the disk is _____________.

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Q. Consider a disk queue with requests for I/O to blocks on cylinders 47, 38, 121, 191, 87, 11, 92, 10. The C-LOOK scheduling algorithm is used. The head is initially at cylinder number 63, moving towards larger cylinder numbers on its servicing pass. The cylinders are numbered from 0 to 199. The total head movement (in number of cylinders) incurred while servicing these requests is:

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Q. Which of the following DMA transfer modes and interrupt handling mechanisms will enable the highest I/O band-width?

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Q. Consider three processes (process id 0, 1, 2 respectively) with compute time bursts 2, 4 and 8 time units. All processes arrive at time zero. Consider the longest remaining time first (LRTF) scheduling algorithm. In LRTF ties are broken by giving priority to the process with the lowest process id. The average turn around time is:

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Q. Consider three processes, all arriving at time zero, with total execution time of 10, 20 and 30 units, respectively. Each process spends the first 20% of execution time doing I/O, the next 70% of time doing computation, and the last 10% of time doing I/O again. The operating system uses a shortest remaining compute time first scheduling algorithm and schedules a new process either when the running process gets blocked on I/O or when the running process finishes its compute burst. Assume that all I/O operations can be overlapped as much as possible. For what percentage of time does the CPU remain idle?

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Q. Consider three CPU-intensive processes, which require 10, 20 and 30 time units and arrive at times 0, 2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.

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Q. Which of the following process scheduling algorithm may lead to starvation

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Q. If the quantum time of round robin algorithm is very large, then it is equivalent to:

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Q. A scheduling algorithm assigns priority proportional to the waiting time of a process. Every process starts with priority zero (the lowest priority). The scheduler re-evaluates the process priorities every T time units and decides the next process to schedule. Which one of the following is TRUE if the processes have no I/O operations and all arrive at time zero?

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Q. Consider the 3 processes, P1, P2 and P3 shown in the table.
Process Arrival time Time Units Required
P1 0 5
P2 1 7
P3 3 4
The completion order of the 3 processes under the policies FCFS and RR2 (round robin scheduling with CPU quantum of 2 time units) are

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Q. Consider the following table of arrival time and burst time for three processes P0, P1 and P2.

Process Arrival time Burst Time
P0 : 0 ms 9 ms
P1 : 1 ms 4 ms
P2 : 2 ms 9 ms

The pre-emptive shortest job first scheduling algorithm is used. Scheduling is carried out only at arrival or completion of processes. What is the average waiting time for the three processes?

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Q. Which of the following statements are true?

I. Shortest remaining time first scheduling may cause starvation
II. Preemptive scheduling may cause starvation
III. Round robin is better than FCFS in terms of response time

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Q. Group 1 contains some CPU scheduling algorithms and Group 2 contains some applications. Match entries in Group 1 to entries in Group 2.

Group I Group II
(P) Gang Scheduling (1) Guaranteed Scheduling
(Q) Rate Monotonic Scheduling (2) Real-time Scheduling
(R) Fair Share Scheduling (3) Thread Scheduling

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Q. An operating system uses Shortest Remaining Time first (SRT) process scheduling algorithm. Consider the arrival times and execution times for the following processes:

Process Execution time Arrival time
P1 : 20 0
P2 : 25 15
P3 : 10 30
P4 : 15 45

What is the total waiting time for process P2?

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Q. Three processes A, B and C each execute a loop of 100 iterations. In each iteration of the loop, a process performs a single computation that requires tc CPU milliseconds and then initiates a single I/O operation that lasts for tio milliseconds. It is assumed that the computer where the processes execute has sufficient number of I/O devices and the OS of the computer assigns different I/O devices to each process. Also, the scheduling overhead of the OS is negligible. The processes have the following characteristics:

Process id tc tio
A : 100 ms 500 ms
B : 350 ms 500 ms
C : 200 ms 500 ms

The processes A, B, and C are started at times 0, 5 and 10 milliseconds respectively, in a pure time sharing system (round robin scheduling) that uses a time slice of 50 milliseconds. The time in milliseconds at which process C would complete its first I/O operation is ___________.

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Q. An operating system uses shortest remaining time first scheduling algorithm for pre-emptive scheduling of processes. Consider the following set of processes with their arrival times and CPU burst times (in milliseconds):

Process : Arrival Time Burst Time
P1 : 0 12
P2 : 2 4
P3 : 3 6
P4 : 8 5

The average waiting time (in milliseconds) of the processes is _________.

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Q. Consider the following set of processes, with the arrival times and the CPU-burst times given in milliseconds

Process: Arrival Time Burst Time
P1 : 0 5
P2 : 1 3
P3 : 2 3
P4 : 4 1

What is the average turnaround time for these processes with the preemptive shortest remaining processing time first (SRPT) algorithm ?

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Q. A uni-processor computer system only has two processes, both of which alternate 10ms CPU bursts with 90ms I/O bursts. Both the processes were created at nearly the same time. The I/O of both processes can proceed in parallel. Which of the following scheduling strategies will result in the least CPU utilization (over a long period of time) for this system ?

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Q. Which of the following scheduling algorithms is non-preemptive?

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Q. Consider a set of n tasks with known runtimes r1, r2, .... rn to be run on a uniprocessor machine. Which of the following processor scheduling algorithms will result in the maximum throughput?

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