Microsoft Transaction Server

Microsoft Transaction Server (MTS) was software that provided services to Component Object Model (COM) software components, to make it easier to create large distributed applications. The major services provided by MTS were automated transaction management, instance management (or just-in-time activation) and role-based security. MTS is considered to be the first major software to implement aspect-oriented programming.

MTS was first offered in the Windows NT 4.0 Option Pack. In Windows 2000, MTS was enhanced and better integrated with the operating system and COM, and was renamed COM+. COM+ added object pooling, loosely-coupled events and user-defined simple transactions (compensating resource managers) to the features of MTS.

COM+ is still provided with Windows Server 2003 and Windows Server 2008, and the Microsoft .NET Framework provides a wrapper for COM+ in the EnterpriseServices namespace. The Windows Communication Foundation (WCF) provides a way of calling COM+ applications with web services. However, COM+ is based on COM, and Microsoft's strategic software architecture is now web services and .NET, not COM. There are pure .NET-based alternatives for many of the features provided by COM+, and in the long term it is likely COM+ will be phased out.

A basic MTS architecture comprises:

COM components that run under the control of the MTS Executive are called MTS components. In COM+, they are referred to as COM+ Applications. MTS components are in-process DLLs. MTS components are deployed and run in the MTS Executive which manages them. As with other COM components, an object implementing the IClassFactory interface serves as a Factory Object to create new instances of these components.

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