# 1.1 Introduction

A distributed system is 

* "... a system in which the failure of a compute you didn't even know existed can render your own computer unsuable" -- Leslie Lamport 
* ... multiple computers communicating via a network
* ... trying to achieve some task together 
* Consists of "nodes" (computer, phone, car, robot, ...) 

Books

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What make a system distributed?

* It's **inherently distributed**: e.g., sending a message from your mobile phone to your friend's phone 
* For **better reliability**: even if one node fails, the system as a whole keeps functioning 
* For **better performance**: get data from a nearby node rather than one halfway round the world 
  * Putting data closer to where the people are 
* To **solve bigger problem:** e.g. huge amounts of data, can't fit on one machine 

Why NOT make a system distributed?

* The trouble with distributed systems 
  * Communication may fail (and we might not even know it has failed)
  * Processes may crash (and we might not know)
  * All of this may happen nondeterminisitically 
* Fault tolerance: we want the system as a whole to continue working, even when some parts are faulty