Basic CS [Honeywell Placement]: Sample Questions 6 - 7 of 9

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Question 6

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What is a real time system?

Explanation

  • Real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.
  • Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics , for example, a real-time program would display objects moving across the screen at the same speed that they would actually move.

Question 7

Basic CS
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What is exponential back off algorithm?

Explanation

  • It is an algorithm used to space out repeated retransmissions of the same block of data, often as part of network congestion avoidance. In a network, where a sending host is able to know when a collision has occurred (that is, another host has tried to transmit) , when it is sending a frame. If both hosts attempted to re-transmit as soon as a collision occurred, there would be yet another collision — and the pattern would continue forever. The hosts must choose a random value within an acceptable range to ensure that this situation doesn՚t happen. An exponential back-off algorithm is therefore used.
  • Examples are the retransmission of frames in carrier sense multiple access with collision avoidance (CSMA/CA) and carrier sense multiple access with collision detection (CSMA/CD) networks, where this algorithm is part of the channel access method used to send data on these networks. In Ethernet networks, the algorithm is commonly used to schedule retransmissions after collisions. The retransmission is delayed by an amount of time derived from the slot time and the number of attempts to retransmit.

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