Basic CS [TCS Placement]: Sample Questions 54 - 56 of 196

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Question 54

Basic CS
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Describe in Detail

Essay▾

What is Error Detection? What are its methods?

Explanation

  • Data can be corrupted during transmission and hence errors must be detacted and corrected.
  • Error detection uses redundancy- by adding extra bits for detecting errors.
  • Error detection refers to the techniques used to detect noise or other impairments introduced into data while it is transmitted from source to destination.
  • Common error detection methods are
    1. Vertical Redundancy Check (VRC)
    2. Longitudinal Redundancy Check (LRC)
    3. Cyclic Redundancy Check (CRC)
    4. Checksum

Question 55

Basic CS
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Write in Short

Short Answer▾

What is RAID?

Explanation

  • It is a method for providing fault tolerance by using multiple hard disk drives. Short for redundant array of independent disks.
  • Was defined as redundant array of inexpensive disks, but now refers to redundant array of inexpensive disks.
  • RAID uses multiple disks to provide fault tolerance, improve performance, or to increase capacity.
  • RAID is used frequently on servers but not necessary for personal computers.

Question 56

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Describe in Detail

Essay▾

What is process migration?

Explanation

  • It is the transfer of sufficient amount of the state of process from one machine to the target machine.
  • Process migration is the relocation of a process from its source node to another destination node.
  • A process can either be migrated before it starts execution on its source node which is called as non-preemptive process or during the course of its execution that is known as preemptive process migration.
  • Preemptive process migration is more costly compared to non-preemptive because the process environment must accompany the process to its new node.
  • Steps involved in process migration:
    1. Process is selected for migration.
    2. Select destination node for the process to be migrated.
    3. Transfer of selected process to the destination node.
      • Migration policy is responsible for first two steps while third step is handles by migration mechanism.
      • Migration of a process is complex that involves handling various activities to meet the requirements for a good process migration.
  • The sub activities involved are:
    1. Freezing the process on its source node and restarting it on destination node
    2. Transferring the processes address space from restarting from its source to destination node.
    3. Forwarding messages meant for the migrant process.
    4. Handling communication between processes that have been placed at different nodes.
      • A preemptive process migration facility allows the transfer of an executing process from one node to another.
      • On the other hand, in system supporting only non-preemptive migration facility, a process can only be transferred prior to beginning its execution.
      • Preemptive process migration is costlier than non-preemptive process migration since the process state, which must accompany the process to its new node, becomes much more complex after execution begins
      Given the Image is Define the Way a Process Migrates from One Node to Another is Shown in the Figure

      Advantages of process migration:

      1. Reducing average response time of processes

        To reduce the average response time of the processes, processes of a heavily loaded node are migrated to idle or underutilized nodes.

      2. Speeding up individual jobs
        • A migration of job to different node is done and executes them concurrently.
        • Migrate a job to a node having a faster CPU or to a node at which it has minimum turnaround time.
        • More speed up more migration cost involved.

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