Making Utilities for MS-DOS :: Microsoft Computers System Software Essays

Making Utilities for MS-DOS These days, when computers play an important role in virtually all aspects of our life, the issue of concern to many programmers is Microsoft's hiding of technical documentation. Microsoft is by far the most important system software developer. There can be no argument about that. Microsoft's MS-DOS operating system has become a de facto standard (IBM's PC-DOS is actually a licensed version of MS-DOS). And this should be so, because these systems are very well written. The people who designed them are perhaps the best software engineers in the world. But making a computer platform that is a de facto standard should imply a good deal of responsibility before the developers who make applications for that platform. In particular, proper documentation is essential for such a platform. Not providing enough documentation for a system that everyone uses can have disastrous results. Think of it, an operating system is useless by itself, its sole purpose is to provide services to applications. And who would be able to develop applications for an operating system if the documentation for that system is confidential and available only to the company that developed it? Obviously, only the company that has developed that operating system will be able to develop software for it. And this is a violation of the Antitrust Law. And now I start having a suspicion that this is happening with Microsoft's operating systems. It should be no secret to anyone that MS-DOS contains a lot of undocumented system calls, data structures and other features. Numerous books have been written on this subject (see bibliography). Many of them are vital to system programming. There is no way to write a piece of system software, such as a multitasker, a local area network, or another operating system extension, without knowing this undocumented functionality in MS-DOS. And, sure enough, Microsoft is using this functionality extensively when developing operating system extensions. For example, Microsoft Windows, Microsoft Network, and Microsoft CD-ROM Extensions (MSCDEX) rely heavily on the undocumented internals of MS-DOS. The reader can ask, "Why do they leave functionality undocumented?" To answer that question, we should look at what this "functionality" actually is. In MS- DOS, the undocumented "functionality" is actually the internal structures that MS-DOS uses to implement its documented INT 21h API. Any operating system must have some internal structures in which it keeps information about disk drives, open files, network connections, alien file systems, running tasks, etc. And MS- DOS (later I'll call it simply DOS) has internal structures too. These structures form the core of undocumented "functionality" in MS-DOS. This operating system also has some undocumented INT 21h API functions, but they