When a call is made to open a connection to SQL Server (dbopen), DB-Library determines which client-side Net-Library should be loaded to communicate with SQL Server.
Net-Libraries are linked dynamically at run time. With the Windows, Windows 95, and Windows NT operating systems, Net-Libraries are implemented as dynamic-link libraries (DLLs), and multiple Net-Libraries can be loaded simultaneously. With the MS-DOS operating system, Net-Libraries are implemented as terminate-and-stay-resident (TSR), and only one can be loaded at any given time.