The key environment variables in DB2 are DB2INSTANCE and DB2NODE. As mentioned in previous post Sharing More Basics, the central repository is the DB2 profile registry. This has nothing to do with the Microsoft Windows registry. The command db2ilist will give you a list of all instances. You have the ability to set any of the profile registry values using environment variables. However it is strongly recommended that you use the db2set command.
The instance is the environment in which databases are contained in DB2. However you should note that dropping an instance does not automatically drop the databases contained in that instance. The default instance is aptly named "DB2" in the Windows version of IBM DB2. The instance level is also known as the Database Manager level.
There is a background process called the Database Administration Server (DAS). It provides the ability to manager the database with GUI tools. In versions of DB2 prior to 8.2, the DAS used to be a separate instance.
