The Query Processor
The bcp utility works in conjunction with the query processor to insert data into an instance of Microsoft® SQL Server™. The bcp utility generates client OLE DB rowsets that are sent to SQL Server and are inserted into the table by the query processor. This has the advantage of allowing the query processor to plan and optimize queries that import and export data from an instance of SQL Server. It also allows optimized index maintenance, constraint checking, and parallel data load operations. The BULK INSERT statement works in conjunction with the query processor to bulk copy data into an instance of SQL Server.
Any program written using the bulk copy API takes advantage of using client OLE DB rowsets and the SQL Server query processor to insert data.