COM: Component Object Model Technologies

What is COM?

Microsoft COM (Component Object Model) technology in the Microsoft Windows-family of Operating Systems enables software components to communicate. COM is used by developers to create re-usable software components, link components together to build applications, and take advantage of Windows services. COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects. The family of COM technologies includes COM+, Distributed COM (DCOM) and ActiveX® Controls.

Microsoft provides COM interfaces for many Windows application programming interfaces such as Direct Show, Media Foundation, Packaging API, Windows Animation Manager, Windows Portable Devices, and Microsoft Active Directory (AD).

COM is used in applications such as the Microsoft Office Family of products. For example COM OLE technology allows Word documents to dynamically link to data in Excel spreadsheets and COM Automation allows users to build scripts in their applications to perform repetitive tasks or control one application from another.

What is COM+?

COM+ is the name of the COM-based services and technologies first released in Windows 2000. COM+ brought together the technology of COM components and the application host of Microsoft Transaction Server (MTS). COM+ automatically handles programming tasks such as resource pooling, disconnected applications, event publication and subscription and distributed transactions.

I want to build a COM or COM+ application. How do I get started?

The best resource for COM developers is the Microsoft Developer Network (MSDN). The MSDN Library contains information for developers on the Microsoft platform including a programming guide for COM development and the COM API programming reference. The Windows API is documented in Win32 and COM Development. You will also find information on COM+.

Using COM from .NET and .NET from COM

The .NET Framework provides bi-directional interoperability with COM, which enables COM-based applications to use .NET components and .NET applications to use COM components. For information on how to access .NET components from COM see http://msdn.microsoft.com/library/ms973802.aspx. To learn how to use COM components from .NET see http://msdn.microsoft.com/library/ms973800.aspx.