Dynamic Data Exchange Protocol

Because the Win32 API has a message-based architecture, passing messages is the most appropriate method for automatically transferring information between applications. However, Win32 messages contain only two parameters (wParam and lParam) for passing data. As a result, these parameters must refer indirectly to other pieces of data when more than a few words of information pass between applications. The DDE protocol defines exactly how applications should use the wParam and lParam parameters to pass larger pieces of data by means of global atoms and shared memory handles. The DDE protocol has specific rules for allocating and deleting global atoms and shared memory objects.

A global atom is a reference to a character string. In the DDE protocol, atoms identify the applications exchanging data, the nature of the data being exchanged, and the data items themselves. For more information about atoms, see Atoms.