YAHOO —> Google two papers, GFS, MapReduce.
hadoop common：Common tools to support other Hadoop modules.
HDFS：Distributed file system provides high throughput access to application data. The full name: Hadoop Distributed File System.
hadoop yarn：A framework for job scheduling and cluster resource management.
hadoop mapreduce：A large data set parallel processing system based on YARN.
ApacheOther Hadoop related projects include:Ambari™，Avro™，Cassandra™，Chukwa™，HBase™，Hive™，Mahout™，Pig™，Spark™，Tez™，ZooKeeper™。
Three: Hadoop isReliable，ExtensibleDistributed computing software, and one more thing isHigh performance，He needs other software to achieve this characteristic.