This document provides an overview of Apache Hadoop, a distributed processing framework for large datasets. It describes how Hadoop uses the Hadoop Distributed File System (HDFS) to provide a unified view of large amounts of data across clusters of computers. It also explains how the MapReduce programming model allows distributed computations to be run efficiently across large datasets in parallel. Key aspects of Hadoop's architecture like scalability, fault tolerance and the MapReduce programming model are discussed at a high level.