There seems to be a conflict in the documentation about what constitutes a "database". Seems that Resource is a *special* system database. Whether it's truly a system database is debatable ...
So I reckon Resource is *not* a system database using following logic:
* SQL Server 2005 BOL ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/tsqlref9/html/60a93880-62f1-4eda-a886-f046706ba90c.htm states for sys.sysdatabases
"Contains one row for each database in an instance of Microsoft SQL Server 2005. When SQL Server is first installed, sysdatabases contains entries for the master, model, msdb, and tempdb databases."
No Resource there.
* Also, trying the following in studio
it failed with:
"Could not locate entry in sysdatabases for database 'Resource'. No entry found with that name. Make sure that the name is entered correctly."
So if it doesn't look like a duck and can't quack like a duck, I reckon it's not a duck.