In a classical sense, if we are to talk of Hadoop then it comprises of two components: a storage layer called HDFS and a processing layer called MapReduce. Resource management task prior to Hadoop 2.X was done using the MapReduce framework of Hadoop itself. However, that changed with the introduction of YARN. In Hadoop 2.0, YARN was introduced as the third component of Hadoop to manage the resources of the Hadoop cluster and make it more MapReduce agnostic.