COM in Windows stands for the Component Object Model. It is a fundamental technology developed by Microsoft that allows software components to interact with each other, regardless of the language they were written in.
Understanding the Component Object Model (COM)
As defined by Microsoft, COM is a platform-independent, distributed, object-oriented system for creating binary software components that can interact. Think of it as a standard way for different pieces of software to communicate and work together on the Windows operating system, and potentially across networks.
Essentially, COM enables developers to build software in smaller, reusable parts (components). These components expose specific functionalities through defined interfaces, allowing other applications or components to access and utilize those functionalities without needing to know the component's internal implementation details.
Key Characteristics of COM
COM is built upon several core principles that make this component interaction possible:
- Platform-Independent: While heavily associated with Windows, the design principles allow for potential implementation on other platforms.
- Distributed: COM evolved to support distributed applications through Distributed COM (DCOM), enabling components to interact across networks.
- Object-Oriented: It utilizes object-oriented principles like encapsulation and polymorphism through interfaces, allowing components to expose objects and methods.
- Binary Standard: This is crucial. COM defines a binary standard, meaning components compiled into binary code (like DLLs or EXEs) can interact if they adhere to the COM specification, regardless of the source code language (C++, Visual Basic, etc.).
- Interface-Based: Interaction happens through well-defined interfaces. Components guarantee they implement specific interfaces, and clients program to these interfaces, not to the specific implementation details.
Here's a simple way to look at some key aspects:
| Aspect | Description |
|---|---|
| What it is | A system for binary software components |
| Purpose | Enabling interaction between components |
| Key Feature | Interface-based communication |
| Independence | Language-independent, aims for platform-independence |
COM as a Foundation Technology
COM is not just an isolated technology; it's the bedrock for several other important Microsoft technologies. According to the reference documentation, COM is the foundation technology for Microsoft's OLE (compound documents) and ActiveX (Internet-enabled components) technologies.
- OLE (Object Linking and Embedding): Enables embedding and linking documents and objects within other documents. For example, embedding an Excel spreadsheet object within a Word document relies heavily on COM.
- ActiveX: Components designed for integration, often associated with web browsers (though usage has changed over time). ActiveX controls are essentially COM components designed for specific environments.
By providing a standard way for components to expose capabilities, COM allowed technologies like OLE and ActiveX to build richer, more interactive experiences by integrating functionalities from different software pieces.
In summary, COM is the vital underlying framework in Windows that makes it possible for different software parts to talk to each other effectively and reliably, forming the basis for many features and other technologies you encounter.
