It All begins with 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 reusable 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.
So 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.
COM+ and DCOM
In order for Microsoft to provide developers with support for distributed transactions, resource pooling, disconnected applications, event publication and subscription, better memory and processor (thread) management, as well as to position Windows as an alternative to other enterprise-level operating systems, Microsoft introduced a technology called Microsoft Transaction Server (MTS) on Windows NT 4. With Windows 2000, that significant extension to COM was incorporated into the operating system (as opposed to the series of external tools provided by MTS) and renamed COM+.
At the same time, Microsoft de-emphasized DCOM as a separate entity. Components that made use of COM+ services were handled more directly by the added layer of COM+, in particular by operating system support for interception. In the first release of MTS, the interception was tacked on - installing an MTS component would modify the Windows Registry to call the MTS software, and not the component directly. Windows 2000 also revised the Component Services control panel application used to configure COM+ components.
At the same time, Microsoft de-emphasized DCOM as a separate entity. Components that made use of COM+ services were handled more directly by the added layer of COM+, in particular by operating system support for interception. In the first release of MTS, the interception was tacked on - installing an MTS component would modify the Windows Registry to call the MTS software, and not the component directly. Windows 2000 also revised the Component Services control panel application used to configure COM+ components.
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