| DCOM Explained by Rosemary Rock-Evans Digital Press ISBN: 1555582168 Pub Date: 09/01/98

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### Distributed File Services

The aim of a distributed file service is to provide one unified integrated file system that can be used by all users to share files and the information in those files across a network of machines running different operating systems. A DFS enables a collection of heterogeneous computers to share files as though all the computers were homogeneous. It is thus a global file system with a single shared file space. The files can contain anything the user wants—text, audio, video, data, etc., but it will obviously need to be interpreted/accessed by whatever package/software created it, where the data format is software defined.

Users should be able to share files, copy files, maintain, update, and remove files, as though they were all local to their machine. Users (end users or developers) should have no need to know that the files are distributed.

Windows NT 4 has a distributed file system, where files in the network are presented as a single hierarchical view, accessible across the network. An even fuller version of the file system with more features is expected in Windows NT version 5.

But the Windows NT DFS is not a cross-operating system. Microsoft did not implement the DCE DFS and has no apparent plans to do so. Furthermore, the vendors porting DCOM to other platforms also have not stated any plans to provide such a service. As such, although Windows NT has a distributed file service, we can say that DCOM does not and is unlikely to get one. Does this matter?

DFS is not a service used by developers to build applications and is thus a sort of periphery service to many people. Many developers consider that middleware should just provide services to build distributed applications and support them at runtime afterwards.

But DFSs are useful. The DCE DFS, for example, has been used to support some of the most demanding file access applications yet developed. IBM’s 1996 Atlanta Olympic information service was underpinned by DFS, and although IBM had problems with the quality of information being entered on the system, it had no problems with providing the information to journalists and reporters across the world, with very acceptable response times.

It is something of a pity, therefore, that Microsoft doesn’t use DCE’s DFS or provide more support for distribution of their own on other operating systems. But we must be careful here about the limitations of Microsoft’s approach. What cannot be achieved via DCOM may be achieved in a different sort of way via the Internet.

Microsoft’s vision is to have a single user interface for all access to server data. Effectively, they want to unify the world of the Internet, intranet, and enterprise so that the same interface is used whatever method of communication is used. That interface will be the Windows interface combined with Microsoft’s Web Browser. Web Browser and Windows will eventually be indistinguishable. The Web Browser will be used to browse the World Wide Web and to browse your PC’s files or the files in PCs of others on the network.

A user, for example, will be able to open files and folders on his or her own machine using the same approach as that used in Web Browsers—so local or remote internal files will look like Internet Web pages. Just like pages in an Internet file, the developer will be able to create internal bookmarks that will enable the end user to jump about the files as they can with Web pages. Users will be able to navigate though the files as though they were Web pages and open them with the same paradigm—a single click as though they were a “hot spot.” A developer, for example, will also be able to create Web pages in HTML (more about this in a later chapter) and include them in the Directory as though they were normal files.

Conversely, Internet pages will look like local files, arranged in a hierarchical way to look like your directory. All Internet files will simply be filed under the Directory heading of “Internet.” In effect, there will be the equivalence of external and internal storage space.

The Internet will appear to be just an extension of your hard disk, with frequently used pages cached or simply accessed invisibly via the Internet through the browser capability. The same task bars will be used to navigate files and the Internet. The Find option on the task bar Start button will enable you to search for information on your hard disk and search for information on the Internet. (For more details see http://www.microsoft.com/ie/ie40/integrat/).

Thus, although Microsoft does not have a Distributed File System which covers several operating systems, they do have a distributed file system—an integrated distributed file system—that covers their operating system and any files on the Internet. Thus, a user could create files on both the internal network and external networks in “Internet format” using HTML pages on operating systems other than Windows NT and access them using the new Windows interface.

By using Microsoft’s approach to distributed files, users should be able to share and look at files but they won’t be able to copy files, maintain, update, and remove files, in the same way that you can with a full distributed file system. Nevertheless, the use of the Internet format as a means of supporting distribution is quite inspired, as the end user is assured of having a common readable format for information.

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