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# System prepended metadata

title: Distributed system | Notes (Part 1)

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# Distributed system | Notes (Part 1)
Def : A distributed system consists of **hardware** and **software** components located in a network of computers that communicate and coordinate their actions only by passing messages.


### Consequences of distributed systems
* Concurrency
    * 多台電腦同時工作
    * 網路延遲不是不變的所以同步化困難(Network delays are not constant make synchronization difficult.)
* No Global Clock
    * When programs need to cooperate they coordinate their actions by exchanging messages.
    * Close coordination often depends on a shared idea of the time at which events occur.
    * There are limits to the accuracy with which components in a network can synchronize their clocks.
    * Direct consequence of the fact that messages are sent through a network and network delays are not constant(or even bounded)
* Independent failures
    * All computer systems can fail it is good design to build robustness in.
    * Distributed systems fail in new ways.
    * Network faults might result in components being isolated but not stopping.
