The document discusses the key components of Hadoop including the NameNode, DataNodes, JobTracker, TaskTracker, and SecondaryNameNode. The NameNode stores metadata about data locations and attributes and is located on the master node. DataNodes store the actual data blocks across slave nodes. The JobTracker schedules jobs and is also located on the master node, while TaskTrackers execute tasks on slave nodes. The SecondaryNameNode assists if the NameNode fails. Hadoop uses a master/slave architecture with the NameNode and JobTracker on the master and DataNodes and TaskTrackers on slave nodes. MapReduce is used for distributed processing where tasks are assigned to nodes and results are aggregated.