What is COM? What is COM +?

What is COM?
The so-called COM (Componet Object Model, Component Object Model) is a specification that describes how to establish dynamically changing components. This SPECIFICATION provides a way to ensure interoperability, some binary and network standards that customers and components should follow. This standard allows communication between any two components without considering whether the operating environment is the same, whether the development languages used are consistent, and whether they run on the same computer.
What are the advantages of COM?
First, users generally want to customize the applications they use, and the component technology is essentially customizable, therefore, users can replace the original one with a component that better meets their needs. Secondly, because components are components independent from applications, we can use the same component in different programs without any problems, and the reusability of the software will be greatly enhanced. Third, with the increase of network bandwidth and its importance, distributed network applications have undoubtedly become an increasingly important part of the software market. The component price structure simplifies the process of developing such applications.

What is COM +?
COM + is not a simple upgrade of COM. The underlying structure of COM + is still based on COM. It covers almost all COM content, COM + integrates the technical elements of COM, DCOM, and MTS. It promotes COM component software to the application layer instead of the underlying software structure. It supports various operating systems, the component object model is built on the application layer and the underlying details of all components are left to the operating system. Therefore, the combination of COM + and the operating system is closer.
COM + is no longer limited to the COM component technology. It focuses more on the design and implementation of distributed network applications. COM + inherits almost all the advantages of COM and avoids some shortcomings in COM implementation. It combines the programming models of COM, DCOM, and MTS and inherits the vast majority of their features, new features are added to the original features.

What are the new advantages of COM +?
The following lists the main features of COM +:

COM + not only inherits all the advantages of COM, but also adds some services, such as queue service, load balancing, memory database, and event service.

The queue service is very meaningful for distributed applications, especially when the network speed is very slow, this mechanism can ensure that the application system can run reliably. When the application system contains a large number of nodes but the server is busy, the customer application can put their requests in the queue and process these requests when the server load ratio is lighter;

Another example is that COM + provides the load balancing service, which can achieve dynamic load balancing. In addition, the load balancing feature of COM + applications does not need to be supported by coding, both client programs and component programs can be implemented in the usual way. The load balancing feature is not implemented by programming, but by configuring Load Balancing for distributed applications. The Queue Service mentioned above, in fact, it also reflects a load balancing.

(1) Real asynchronous communication. The underlying layer of COM + provides Queue component services, which makes it possible for customers and components to work collaboratively at different time points. COM + applications can achieve this feature without adding code.

(2) Event Service. The new event mechanism makes the event source and event receiver more flexible in implementing the event function. The system service simplifies the event model and avoids the trivial details of the object mechanism that can be connected to COM.

(3) scalability. The scalability of COM + comes from multiple aspects. Dynamic Load Balancing, memory database, Object pool, and other system services provide the technical basis for the scalability of COM +, the scalability principle of COM + is consistent with that of the multi-layer structure.

(4) manageability and configurability. Management and configuration are actions after the application system is developed. As the software maintenance costs keep increasing, COM + applications will help software vendors and users Reduce investment in this area.

(5) easy to develop. The complexity and difficulty of COM + application development determine the success or failure of COM +. Although the COM + development model is simpler than the previous COM component development model, however, some excellent development tools are still needed to improve development efficiency.

COM + marks that Microsoft's component technology has reached a new height. It is no longer limited to a desktop system on a machine. It directs its goal to a broader enterprise intranet, or even the Internet. COM + and multilayer structure model and Windows operating system provide a complete set of solutions for enterprise applications or Web Applications