COM+

COM+
Name	COM+
Developer	Microsoft
Initial release	1996
Latest release	Integrated into Windows Server and .NET ecosystem
Written in	C, C++
Operating system	Microsoft Windows
Genre	Component software, middleware
License	Proprietary

COM+

COM+ is a component-based middleware technology introduced by Microsoft to extend distributed component architectures on Windows. It built on prior component models to provide runtime services, eventing, and integration for enterprise applications, supporting transactional processing, security, and object pooling. COM+ was influential in the evolution of distributed systems alongside contemporaries from other vendors and standards bodies.

Overview

COM+ emerged as an evolution of component models such as Component Object Model and as a successor to Microsoft Transaction Server, aiming to unify services for enterprise applications on Microsoft Windows NT and later Windows 2000. Designed to interoperate with technologies like DCOM, MTS, and later to coexist with .NET Framework, it targeted scenarios in banking, telecommunications, and large-scale enterprise information systems deployed on Windows Server platforms. The platform competed for adoption with middleware products from IBM, BEA Systems, Oracle Corporation, and standards promoted by Object Management Group and World Wide Web Consortium participants.

Architecture and Components

COM+ architecture centers on component activation, runtime hosts, and a catalog of administrative settings managed by the Registery-based catalog and the COM+ Catalog service. Core parts include the COM runtime, the Service Control Manager on Windows NT, and the Component Services administrative snap-in introduced in Microsoft Management Console. Key components and subsystems reference concepts used by Microsoft Visual Studio, Internet Information Services, and Remote Procedure Call mechanisms. Integration points allow COM+ components to be invoked from VBScript, Visual Basic, C++, and from managed code hosted in Internet Information Services application pools. The architecture supports role-based access patterns analogous to designs in Windows Security Model and interacts with directory services such as Active Directory for deployment and policy.

Services and Features

COM+ provides built-in services including automatic transaction demarcation via the Distributed Transaction Coordinator, object pooling inspired by patterns used in Enterprise JavaBeans implementations by Sun Microsystems, queuing through Microsoft Message Queuing, and eventing via the COM+ Event System. Additional features include role-based security integration, load balancing support when combined with Network Load Balancing, and resource management compatible with Windows Performance Monitor. COM+ addressed scalability and reliability concerns similar to those tackled by Tandem Computers and BeOS-era fault-tolerant systems, offering consistent activation semantics used in enterprise resource planning deployments by vendors such as SAP and Siebel Systems.

Development and Programming Model

Developers built COM+ components using languages and tools such as C++, Visual Basic, Delphi (software), and later interfaced from C# and other languages supported by the .NET Framework via interop. The programming model emphasized interfaces, reference counting, and apartment threading models documented alongside Microsoft Developer Network guidance. Developers used Microsoft Visual Studio and tools like the OLE/COM Object Viewer for type library inspection, leveraging IDL files compatible with the Microsoft Interface Definition Language. Patterns from component-oriented design appeared in examples published by authors associated with Addison-Wesley and O'Reilly Media.

Security and Transaction Management

Security in COM+ used role-based access control mapped to Windows Security accounts and Active Directory principals, enabling assignment of roles and privileges at component installation time in the Component Services MMC. Transaction management relied on the Microsoft Distributed Transaction Coordinator to coordinate two-phase commits across resource managers such as Microsoft SQL Server, Oracle Database, and IBM DB2. COM+ supported transaction attributes like Required, RequiresNew, and Supported, paralleling constructs later standardized in enterprise frameworks such as Java Transaction API. Auditing and authentication could be integrated with Kerberos techniques used across Windows Server domains and with policy frameworks used by enterprises like General Electric and IBM.

Deployment and Administration

Administrators deployed COM+ applications using the Component Services snap-in in Microsoft Management Console, command-line tools, or scripted via Windows Script Host and PowerShell in later releases. Deployment metadata was stored in the COM+ Catalog and the Windows Registry with options for exporting application packages as installation files compatible with configuration management practices used by HP and Dell EMC. Administration tasks included configuring pooling, threading, role assignments, and transaction timeouts, and integrating with monitoring tools such as System Center and Windows Event Log. High-availability deployments often combined COM+ components with Cluster Server solutions and network appliances from vendors like Cisco Systems.

Legacy, Compatibility, and Adoption

COM+ saw widespread adoption in the late 1990s and early 2000s across enterprises that standardized on Microsoft Windows Server and Internet Information Services. Over time, its role shifted as the .NET Framework and ASP.NET provided managed alternatives and as microservices architectures promoted by Netflix and Amazon Web Services changed deployment models. Compatibility layers such as COM Interop and runtime hosting enabled integration with CLR-based applications and legacy systems from Siemens and Honeywell. Academic and industry discourse compared COM+ to middleware from Sun Microsystems, Oracle Corporation, and research platforms from Carnegie Mellon University and MIT. While new greenfield development favors managed or containerized frameworks, many mission-critical systems from banks, telecoms, and government agencies continue to run components that rely on COM+ services. Category:Microsoft technologies