Distributed Computing Introduction Definition of Distributed Systems 1. Collection of independent entities cooperation to collectively solve a task. 2. Autonomous processors communicating over a communication network Characterization of Distributed Systems • Crash of a single computer does not inhibit normal operation • Computers • Not sharing common memory, common clock • Communicate by message passing over a network • Run their own operating systems • Semi-autonomous • Loosely coupled • Collection of independent computers • Appearing to users as a single coherent system • Describes a wide range of computers • Weakly coupled systems like WAN's • Strongly coupled systems like LAN's • Very strongly coupled systems like multiprocessor systems Features of Distributed System • No common physical clock • Introduces “distributi