Microsoft TechNet frequently releases White Papers on SQL Server Technology. I have read the following two white papers recently. The summary of its content is here.
Writer: Danny Tambs
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As databases become larger and larger, the infrastructure assets and technology that provide availability become more and more important. The database filegroups feature introduced in previous versions of SQL Server enables the use of multiple database files in order to host very large databases (VLDB) and minimize backup time. In SQL Server 2005 specific files can be set to offline or online.
Reference : Pinal Dave (http://blog.SQLAuthority.com)