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Q:

What are necessary conditions for dead lock?

Answer

1. Mutual exclusion (where at least one resource is non-sharable)


2. Hold and wait (where a process holds one resource and waits for other resource)


3. No preemption (where the resources can’t be preempted)


4. Circular wait (where p[i] is waiting for p[j] to release a resource. i= 1,2,…n


j=if (i!=n) then i+1


else 1 )

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Subject: Operating Systems

Q:

If x is chosen at random from the set {1,2,3,4} and y is to be chosen at random from the set {5,6,7}, what is the probability that xy will be even?

A) 1/2 B) 2/3
C) 3/4 D) 4/3
 
Answer & Explanation Answer: B) 2/3

Explanation:
 

S ={(1,5),(1,6),(1,7),(2,5),(2,6),(2,7),(3,5),(3,6),(3,7),(4,5),(4,6),(4,7)}
Total element n(S)=12

xy will be even when even x or y or both will be even.
Events of x, y being even is E.
E ={(1,6),(2,5),(2,6),(2,7),(3,6),(4,5),(4,6),(4,7)}
n(E) = 8

P(E)=n(E)n(S)=812 = 4/3
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Filed Under: Probability

Q:

There are four hotels in a town. If 3 men check into the hotels in a day then what is the probability that each checks into a different hotel?

A) 1/2 B) 3/4
C) 4/7 D) 3/8
 
Answer & Explanation Answer: D) 3/8

Explanation:

Total cases of checking in the hotels = 4 x 4 x 4 = 64 ways.

Cases when 3 men are checking in different hotels = 4×3×2 = 24 ways.

Required probability =24/64  = 3/8

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Filed Under: Probability

Q:

What is CPU Scheduler?

Answer

Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. All other scheduling is preemptive.

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Subject: Operating Systems

Q:

A card is drawn from a pack of 52 cards. The card is drawn at random. What is the probability that it is neither a spade nor a Jack?

A) 9/13 B) 4/13
C) 10/13 D) 8/13
 
Answer & Explanation Answer: A) 9/13

Explanation:
 

There are 13 spade and 3 more jack


Probability of getting spade or a jack:
=13+352=1652=413

 

So probability of getting neither spade nor a jack:
=1−413 = 9/13
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Filed Under: Probability

Q:

What is Dispatcher?

Answer

Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves: Switching context, Switching to user mode, Jumping to the proper location in the user program to restart that program, dispatch latency – time it takes for the dispatcher to stop one process and start another running.

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Subject: Operating Systems

Q:

What is DRAM? In which form does it store data?

Answer

DRAM is not the best, but it’s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it’s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

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Subject: Operating Systems

Q:

What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

Answer

Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.


 


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Subject: Operating Systems