The breadth of a distributed query/transaction increases the reach of SQL Server to many varied datasources. This power can be extraordinary, but it can be abused if not done properly. It is critical to understand the behavior of a distributed query/transaction so that each affected datasource is kept intact at all times. The MS DTC plays the major role in this capability by controlling the UOW. By implementing a robust two-phase commit protocol environment, Microsoft has provided developers with a safe and fairly simple way to use distributed data regardless of its location in your company. From here, you will head into the world of SQL Server internals and see how SQL Server has been put together to handle concurrent processing, many simultaneous users, large data volumes , and security.