A distributed system is a collection of individual computing devices, interconnected via a network, cooperate to solve a problem. Usually the problem cannot be solved individually. The systems include VLSI chip, shared memory multiprocessor, local area cluster of workstations and Internet. These processors are mostly autonomous.

While parallel processing use all the processors to perform a single task, each processor in distributed system has its own semi-independent agenda. Moreover these processors coordinate their actions in order to share resources and to achieve fault tolerance. The computers in this system will appear as a single coherent computer to the user.

Features of distributed systems

 

• No common physical clock

  It is not possible to synchronize the clocks of multiple processors due to uncertainty in communication delays among them.

 

• No shared memory

  It is not possible for a processor to know the global state of the system.
  

 

• Geographical separation

  Processors are geographically separated while they are connected to networks such as WAN or network cluster of workstations (NOW/COW).
  

 

• Autonomy and heterogeneity

  The loosely coupled processors have different speeds and can run different operating systems.