computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...

, Dynamic Data Exchange (DDE) is a technology for

interprocess communication In computer science, interprocess communication (IPC) is the sharing of data between running processes in a computer system. Mechanisms for IPC may be provided by an operating system. Applications which use IPC are often categorized as clients ...

used in early versions of

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

and

OS/2 OS/2 is a Proprietary software, proprietary computer operating system for x86 and PowerPC based personal computers. It was created and initially developed jointly by IBM and Microsoft, under the leadership of IBM software designer Ed Iacobucci, ...

. DDE allows programs to manipulate objects provided by other programs, and respond to user actions affecting those objects. DDE was partially superseded by

Object Linking and Embedding Object Linking and Embedding (OLE) is a proprietary technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control Extension (OCX), a way to develop and use custom user ...

(OLE), and is currently maintained in Windows systems only for the sake of

backward compatibility In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with Input ...

History and architecture

Dynamic Data Exchange was first introduced in 1987 with the release of Windows 2.0 as a method of

so that one program could communicate with or control another program, somewhat like Sun's RPC (Remote Procedure Call). At the time, the only method for communication between the operating system and client applications was the "Windows Messaging Layer." DDE extended this protocol to allow peer-to-peer communication among client applications, via message broadcasts. Because DDE runs via message broadcasts, it is vulnerable to any window-management code that does not pump messages. This problem was not considered during the design of DDE, because DDE predates

pre-emptive multitasking In computing, preemption is the act performed by an external scheduler — without assistance or cooperation from the task — of temporarily interrupting an executing task, with the intention of resuming it at a later time. This preemptive s ...

in Microsoft Windows. Moreover, any code managing a window handle can respond to a DDE broadcast; the initiator of DDE must distinguish between expected and unexpected responses. DDE interlocutors usually express what information they seek in terms of hierarchical

string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

keys. For example, a cell in

Microsoft Excel Microsoft Excel is a spreadsheet editor developed by Microsoft for Microsoft Windows, Windows, macOS, Android (operating system), Android, iOS and iPadOS. It features calculation or computation capabilities, graphing tools, pivot tables, and a ...

was known to DDE by its "application" name. Each application could further organize information by groups known as "topic" and each topic could serve up individual pieces of data as an "item". For example, if a user wanted to pull a value from Microsoft Excel which was contained in a spreadsheet called "Book1.xls" in the cell in the first row and first column, the application would be "Excel", the topic "Book1.xls" and the item "r1c1". Internal changes in the cell due to Excel actions would then be signaled (in reverse) to the calling application via additional message broadcasts.

Relationship to modern automation technologies

The common use of DDE is for custom-developed applications to control off-the-shelf software. For example, a custom in-house application might use DDE to open a

spreadsheet and fill it with data, by opening a DDE conversation with Excel and sending it DDE commands. This feature has mainly been superseded by the

Component Object Model Component Object Model (COM) is a binary-interface technology for software components from Microsoft that enables using objects in a language-neutral way between different programming languages, programming contexts, processes and machines ...

suite of technologies. Microsoft has not used DDE internally since the release of

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

. For example, Excel now exposes an extensive

OLE Automation In Microsoft Windows applications programming, OLE Automation (later renamed to simply Automation) is an inter-process communication mechanism created by Microsoft. It is based on a subset of Component Object Model (COM) that was intended for use ...

object model, which is the recommended method for communicating with Excel. The technique is, however, still in use, particularly for distribution of financial data. Because DDE does not require more operating system components than a conventional Windows GUI program, it is also a ittle-usedalternative for programs seeking to minimize their dependencies.

NetDDE

Wonderware developed an extension for DDE called NetDDE that could be used to initiate and maintain the network connections needed for DDE conversations between DDE-aware applications running on different computers in a network and transparently exchange data. A DDE conversation is an interaction between client and server applications. NetDDE could be used along with DDE and the DDE management library (DDEML) in applications.

/Windows/SYSTEM32

    DDESHARE.EXE ''(DDE Share Manager)''

    NDDEAPIR.EXE ''(NDDEAPI Server Side)''

    NDDENB32.DLL ''(Network DDE NetBIOS Interface)''

    NETDDE.EXE ''(Network DDE - DDE Communication)''

The NetDDE library files Microsoft licensed a basic ( NetBIOS Frames only) version of the product for inclusion in various versions of Windows from

Windows for Workgroups Windows 3.1 is a major release of Microsoft Windows. It was released to manufacturing on April 6, 1992, as a successor to Windows 3.0. Like its predecessors, the Windows 3.1 series run as a Shell (computing), shell on top of MS-DOS; it was t ...

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct successor to Windows 2000 for high-end and business users a ...

. In addition, Wonderware also sold an enhanced version of NetDDE to their own customers that included support for

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

. The technology is extensively used in the

SCADA SCADA (an acronym for supervisory control and data acquisition) is a control system architecture comprising computers, networked data communications and graphical user interfaces for high-level supervision of machines and processes. It also cove ...

field. Basic Windows applications using NetDDE are Clipbook Viewer, WinChat and Microsoft Hearts. NetDDE was still included with

Windows Server 2003 Windows Server 2003, codenamed "Whistler Server", is the sixth major version of the Windows NT operating system produced by Microsoft and the first server version to be released under the Windows Server brand name. It is part of the Windows NT ...

and

Service Pack 2, although it was disabled by default. It has been removed entirely in

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

.NetDDE has been removed in Windows Vista.
/ref> However, this will not prevent existing versions of NetDDE from being installed and functioning on later versions of Windows.

References

Sources

* Charles Petzold. "Dynamic Data Exchange" in ''Programming for Windows 95''. Microsoft Press.

External links