In a Systems Management Server hierarchy, at least one Server License for a SQL Server is required and must be purchased separately. A Server License for Windows NT Server is also required for each server using server code (such as primary, secondary, and helper) for a Systems Management Server. Therefore, if you need to purchase Server Licenses to run three server products (Systems Management Server, SQL Server, and Windows NT Server) on the same computer, it is cheaper to purchase the BackOffice Server License.