Distributed Systems

What is a distributed system?

• A system in which hardware or software components located at networked computers communicate and coordinate their efforts

• A collection of independant computers that appears to its users as a single computer.

Key Aspects

• a number of components

• communication between components

• achieve more than the simple sum of individual components

Computer Networks vs Distributed Systems

Computer Network : Is a collection of spatially seperated, interconnected computer that exchange messages based on specific protocols. Computers are addressed by IP addresses.

Distributed System : Multiple computers on the network working together as a system. The spatial seperation of computers and communication aspects are hidden from users.

Why Distributed Systems?

Resource sharing

• Hardware

• Software

• Other (Processing power, memory, bandwidth)

Benefits of resource sharing

• Economy

• Reliability

• Availability

• Scalability

Consequences of Distributed Systems

• Concurrency : In a distributed system computers perform their tasks autonomously and communicate with other computers. Services provided by distributed systems will be accessed by multiple users. Distributed systems should take this into consideration.

• No global clock : Clocks on individual computers operate independantly. There are limits to the accuracy with which computers in the system can synchronize their clocks.

• Independant failures : Some components may fail while others are running. Failures of participating computers of the system is not known to others immediately.