Distributed Computing: - not everything centralized - many processors

Distributed Systems: Internet The machines of our department ATM machines, bank accounts

What is then parallel computing? Many processors in the same machine All processors solve the same task A restricted form of distributed computing

Basic Distributed Systems: Message passing Shared Memory

Message Passing Systems Easy to implement in hardware

Shared Memory Systems Harder to implement in hardware Easy to program

Distributed Algorithms Several problems: Communication Problems Coordination Problems Specific problems

Example: The counting problem Shared variable Sequential Bottleneck!!!

A better solution: Counting network many shared variables

Example: Routing Problems

Example: Finding the spanning tree problem

Example: Leader election problem

Example: Mutual Exclusion Problem Critical Region One processor allowed

Example: Consensus Problem Time 0 Final Time 1 1 1 1 1 1 1 1 1

Topics: Message Passing Model Spanning Trees Independent Set Coloring Clustering Shared Memory Mutual Exclusion Byzantine Agreement Consensus Distributed Counting