# You asked: What is physical and logical clock?

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## What is physical clock and logical clock?

A logical clock is a mechanism for capturing chronological and causal relationships in a distributed system. Distributed systems may have no physically synchronous global clock, so a logical clock allows global ordering on events from different processes in such systems.

## What is physical clock?

A physical clock is a physical process coupled with a method of measuring that process to record the passage of time. … Most physical clocks are based on cyclic processes (such as a celestial rotation). One or more physical clocks are used to establish a time-line clock for a temporal database.

## What is a physical clock in distributed system?

The physical clocks are used to adjust the time of nodes. Each node in the system can share its local time with other nodes in the system. The time is set based on UTC (Universal Time Coordination). UTC is used as a reference time clock for the nodes in the system.

## How does a logical clock work?

A Lamport logical clock is a numerical software counter value maintained in each process. Conceptually, this logical clock can be thought of as a clock that only has meaning in relation to messages moving between processes. When a process receives a message, it re-synchronizes its logical clock with that sender.

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## What do you mean by logical clock?

A logical clock is a mechanism for capturing chronological and causal relationships in a distributed system. … Moreover, in these applications, it suffices for the processes to agree on the event ordering (i.e., logical clock) rather than the wall-clock time.

## What is clock synchronization and why it is needed?

Clock synchronization is necessary for the ordering of events and to preserve the state of resources. As per algorithms, we can say that for clock synchronization there is need to consider propagation time of messages among each node in both types of algorithms centralized and distributed.

## Why is synchronization necessary?

Synchronization is important because it checks for the differences between two data containers in order to avoid the unneeded transfer of data that already resides in both data sources. Therefore, synchronization schemes typically update both data sources by transferring only additions, changes, and deletions.

## What is use to run the clock in system?

Crystal Oscillator uses a piezoelectric crystal to generate signals. … Generally the oscillator frequency is set to 32.768 KHz, because this is the frequency used in clocks and hence setting of system clock and timers is convenient. The powering of a Real Time Clock is done by a Lithium battery generally.

## What are the types of distributed systems?

Types of Distributed Operating System

• Client-Server Systems.
• Peer-to-Peer Systems.
• Middleware.
• Three-tier.
• N-tier.

## What are the characteristics of a distributed file system?

Desirable features of a distributed file system:

• Transparency. – Structure transparency. …
• User mobility. Automatically bring the user s environment (e.g. user s home directory) to the node where the user logs in. …
• Performance. …
• Simplicity and ease of use. …
• Scalability. …
• High availability. …
• High reliability. …
• Data integrity.
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