There is nothing sacred about electrons being called negative charge and protons positive charge.Itâs just a convention. You, can very well call electrons as positive charge and protons as negative charge!
Single Node or Psuedo-Distributed Cluster is the one in which all the essential daemons (like NameNode, DataNode, JobTracker and TaskTracker) run on the same machine. The default replication factor for a single node cluster is 1. A single node cluster is basically used to simulate a full cluster like environment and to test hadoop applications and unlike the Stand-alone mode, HDFS is accessible in this.
Operating System runs on one of the nodes and controls the activities of other nodes. For more on Clusters, refer the Wiki Page. What is a Beowulf Cluster. Beowulf Clusters are cheap clusters created using off the shelf components. You can create a Beowulf cluster with just a few crap computers and an ethernet segment in your backyard. Although they don't give you top-notch performance, their performance is many-fold better than a single computer. A variant of Beowulf Clusters allows OS to run on every node and still allow parallel processing.