Basic CS-Operating System [3i Infotech Placement]: Sample Questions 31 - 32 of 89

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Question 31

Operating System
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Describe in Detail

Essay▾

What is logical volume group?

Explanation

  • Logical volume group or LVM A relatively new approach to UNIX disks and file systems.
  • Provides abstraction layer between operating system and physical hard drives.
  • Provides a virtual disk space which can be flexibly mapped to real physical disks.
  • The commands in LVM are very similar to the actual physical disks.

Every valid command is preceded by physical volume and volume group as shown below:

  • Physical Volume = pv
  • Volume Group = vg
  • Logical Volume = lv
Physical Volume and Volume Group

Advantages of logical volume group.

  • Offer greater flexibility for disk partitioning.
  • Size of logical volumes can be modified according to need, while the operating system is running
  • Logical volumes can span multiple disks.
  • Disk mirroring is often supported, for greater data reliability

Question 32

Operating System
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Describe in Detail

Essay▾

What are turnaround time and response time?

Explanation

Response Time and Turnaround Time

Turn Around Time

  • The sum total of waiting time & execution time is known as the turnaround time.
  • The time a given process takes from submission to completion.
  • Example: order of arrival of process P1, P2, P3 was sequential with each taking 5,15, 10 second respetively.
    • First process takes s 5 seconds to finish from submission to completion.
    • Second process takes 5 + 15 = 20, seconds from submission to completion- Add 5 because P2 has waited for P1 to finish.
  • Same, the third process takes 5 + 15 + 10 = 30 seconds from submission to completion.
    • The third process has to wait for both P1 and P2 to finish.
  • The average turnaround time is seconds.
  • We change algorithm from first come first serve to some other scheduling algorithm.
  • We think of the turnaround time as the sum of waiting time and execution time.

Response Time

  • The time from the submission of a request to the time of first response by the CPU.
  • The time difference between the issuance of a command and the start of a response to command.
  • Deceptively similar to waiting time but it is time the given process takes after leaving the ready state until it gets attention of the CPU depending on which scheduling algorithm.
  • Useful in interactive systems for understanding the time between issue of command beginning of the output.
  • In other words, it is time difference between arrival and the first execution.

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