3.0 uses either SQL Server Express or Windows Internal Database as its database engine, whereas WSUS 2.0 uses WMSDE. System Center Configuration Manager (SCCM) interoperates with WSUS and can import third party security updates into the product. Licensing WSUS is a feature of the Windows Server product and therefore requires a valid Windows Server license for the machine hosting the service. The fact that user workstations authenticate themselves on the WSUS service to retrieve their updates makes it necessary to acquire a fileserver client access license (CAL) for each workstation connecting to the WSUS service. Fileserver CAL for WSUS is the same CAL as the one required for connecting to a Microsoft Active Directory, fileserver and printserver, and has to be acquired once for a device or a user. WSUS is often considered as a free product because fileserver CAL are already paid for in an enterprise network that has a Microsoft Active Directory and thus do not need to be acquired again. In a network using Samba Active Directory, it is not necessary to purchase CALs to connect to the domain controller or connect to a Samba file server. However, the use of a WSUS server will still require the purchase of client access licenses for all Windows workstations that will connect to the WSUS server. Version history References External links on Microsoft Docs Windows Server Microsoft server technology Patch utilities