Component Object Model - History

History

One of the first methods of interprocess communication in Windows was Dynamic Data Exchange (DDE), first introduced in 1987, that allowed sending and receiving messages in so-called "conversations" between applications.

Antony Williams, one of the most notable thinkers involved in the creation of the COM architecture, later distributed two internal papers in Microsoft that embraced the concept of software components: Object Architecture: Dealing With the Unknown – or – Type Safety in a Dynamically Extensible Class Library in 1988 and On Inheritance: What It Means and How To Use It in 1990. These provided the foundation of many of the ideas behind COM.

Object Linking and Embedding (OLE), Microsoft's first object-based framework, was built on top of DDE and designed specifically for compound documents. It was introduced with Word for Windows and Excel in 1991, and was later included with Windows, starting with version 3.1 in 1992.

An example of a compound document is a spreadsheet embedded in a Word for Windows document: as changes are made to the spreadsheet within Excel, they appear automatically inside the Word document.

In 1991, Microsoft introduced Visual Basic Extensions (VBX) with Visual Basic 1.0. A VBX is a packaged extension in the form of a dynamic-link library (DLL) that allowed objects to be graphically placed in a form and manipulated by properties and methods. These were later adapted for use by other languages such as Visual C++.

In 1992, when version 3.1 of Windows was released, Microsoft released OLE 2 with its underlying object model. The COM Application binary interface (ABI) was the same as the MAPI ABI, which was released in 1992. While OLE 1 was focused on compound documents, COM and OLE 2 were designed to address software components in general. Text conversations and Windows messages had proved not to be flexible enough to allow sharing application features in a robust and extensible way, so COM was created as a new foundation, and OLE changed to OLE2.

In 1994 OLE custom controls (OCXs) were introduced as the successor to VBX controls. At the same time, Microsoft stated that OLE 2 would just be known as "OLE", and that OLE was no longer an acronym, but a name for all of the company's component technologies.

In early 1996, Microsoft found a new use for OLE Custom Controls, expanding their Web browser's capability to present content, renamed some parts of OLE relating to the Internet ActiveX, and gradually renamed all OLE technologies to ActiveX, except the compound document technology that was used in Microsoft Office. Later that year, DCOM was introduced as an answer to CORBA.