System Data Type
This field displays the SQL system data type, which is the type of data that the column can contain. This field is derived from the Data Type field.
For example, the user-defined data type CurrentDateType is based on the system data type datetime. So if CurrentDateType is the Data Type, the System Data Type field displays datetime.
If the Data Type field specifies a system data type, then the system data type is also displayed in the System Data Type field.
For more information about data types, see the SQL Server online help.