A common approach to simplifying client side installation can be summarized under the buzzword "thin client": the less functionality that resides on the client, the fewer installation and maintenance problems can occur.
However, the "thinner" the client components, the less user-friendly the overall application, and the higher the demands to both network and server. Also, thin clients do not take advantage of the significant computing power already available on today's desktops, which is not likely to decrease for most users because desktop productivity applications like word processors or spreadsheets are inherently monolithic. Choosing the right level of "thickness" is thus a critical decision in the design of a distributed application.
DCOM helps in making this tradeoff between flexibility and ease of deployment by letting developers and even administrators choose the location of individual components. The same business components (for example, data entry validation) can be run on the server or on the client with a simple change of configuration. The application can dynamically choose which user interface component to use (HTML generator on the server or ActiveX control on the client).
The biggest problem for maintaining "fat" clients is updating those clients to newer versions. As of today, Microsoft Internet Explorer 3.0 provides an elegant solution to this problem with its support for code downloading. Whenever a user browses to a page, Microsoft Internet Explorer checks the version of the ActiveX controls used on the page and updates them automatically if needed. Applications can also use this support directly (the ActiveX CoCreateClassFromURL function) without explicitly using a browser.
In Windows NT 5.0, the concept of code download will be extended to the concept of a native COM class store. This class store will use the extended directory to store configuration information about components, including references to the actual code, conceptually extending the local registry as used today. The class store will effectively provide both Intranet (extended directory) and Internet (code download, Internet search-path) code repositories, making them completely transparent to existing applications.
Installing and updating the server components is usually a much less critical problem. However, in a highly distributed application, it is often not possible to upgrade all clients simultaneously. DCOM's robust versioning support, described in Section 0, "Evolving Functionality: Versioning,") allows servers to expose new functionality while maintaining complete backward compatibility. A single server component can handle both old and new clients. Once all clients are updated, the component can phase out support for the functionality that is not needed by the new clients.
With both code-download and its future extension, the class store, administrators can centrally install and upgrade clients efficiently and robustly, making it possible to migrate from "fat" clients to intelligent clients without thinning out too much functionality. DCOM's support for robust versioning makes it possible to update servers without previously updating all potential clients.