X Server 
The X server (Remote SQL Server) is the communication instance of the SAP DB software when the individual components are located on different computers.
· Database applications and servers of the SAP DB tools (for example, Loader) address the X server when they want to establish a connection with a database instance installed on another computer.
· Clients of the SAP DB tools (for example, DBMCLI, LOADERCLI) address the X server when they want to establish a connection with a SAP DB tool server (for example, DBM Server, Loader) installed on a different computer.
Each time a connection is successfully established, an additional X server instance is started (Windows: Thread, UNIX: Process). This X server instance is needed to transport the data packages across the network. When the connection ends, the X server instance is closed.
See also:
Architecture of the Database Manager
Architecture of the SAP DB Loader