An entity (e.g. a computer or a program) in a distributed system which is used to simplify implementing global tasks by solving them in a centralized way. A global task is an operation which has to provide a consistent view of information distributed over all nodes in the system or has to coordinate all nodes for some other reasons.
Using a central node allows to use classic, non-distributed algorithms to provide the result but has disadvantages since the node is a bottleneck and a single point of failure. Some approaches (e.g. Sun's NIS) try to
alleviate those problems by providing backup nodes.
| 
