For the Win32-based versions of the DB-Library dynamic-link library (DLL), a separate operating-system thread may be spawned for each connection that DB-Library makes with SQL Server (depending on the Net-Library in use). Each instance of the DB-Library DLL loaded by a calling process gets a private data area, while sharing code.
Win32-based DB-Library architecture differs from the implementation with the Windows operating system. In Windows, MSDBLIB3.DLL maintains DB-Library connections as a linked list of connections in a single data segment. This architecture is required because in the Windows operating system, dynamic-link libraries have a single data segment that is shared among all calling processes. This necessitates the initialization and clean up of the DB-Library DLL data structures through calls to the dbinit and dbwinexit functions. Because dbinit initializes private DB-Library structures and to maintain compatibility with future versions of DB-Library, you should call dbinit for all environments.