Using database filegroups
You can group data files for a database into filegroups for allocation and administration purposes. In some cases, you can improve performance by controlling the placement of data and indexes into specific filegroups on specific drives or volumes. The filegroup containing the primary data file is called the primary filegroup. Only one primary filegroup exists, and if you don’t ask specifically to place files in other filegroups when you create your database, all your data files end up in the primary filegroup.
In addition to the primary filegroup, a database can have one or more user-defined filegroups, which you can create by using the FILEGROUP keyword in the CREATE DATABASE or ALTER DATABASE statement.
Don’t confuse ...