Basic CS-Operating System [3i Infotech Placement]: Sample Questions 57 - 58 of 89

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Question 57

Operating System

Describe in Detail


What is time-stamping?


Time-Stamp Based Protocols
  • Time-stamping is the technique proposed by lamppost to order events in a distributed system without the use of clocks.
  • Scheme is used to order events consisting of the transmission of messages.
  • Any event or activity can have its timestamp recorded, depending on the needs of the user or the capabilities of the system process creating the timestamp.
  • Essential for synchronization for most computer related processes.
  • For example, modify timestamps on files requiring backups are essential so that the backup be only taken for files changed or referenced.
  • Timestamps recorded automatically by the operating system are file creation and file modification.
  • The problem with timestamp is when synchronizing event or message across two devices.

Question 58

Operating System



A MB PCM (Pulse Code Modulation) has


Choice (4)


channels out of which voice channel, signalling channel, & synchronization channel.




voice channels & signalling channel.


voice channels & signalling channel.




Block Diagram of PCM
  • The Pulse Code Modulation process is done in three steps Sampling, Quantization, and Coding.
    • A MB PCM (Pulse Code Modulation) has voice channels & signalling channel.
    • PCM is a digital representation of an analogue signal with samples of the amplitude at regular intervals.
    • This digital sampled analog data can then be changed to binary data.
  • PCM requires a very accurate clock.
  • The number of samples per second must be from to - usually several times the maximum frequency of the analog waveform in Hertz (Hz) , or cycles per second, which ranges from KHz.
  • Analog signal can be reproduced by demodulation.

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