Реферат: Making Utilities For MSDOS Essay Research Paper

Undocumented DOS Andrew Schulman suggests that Microsoft could make an add-in to

MS-DOS that would provide “clean” documented services that would eliminate the

need for the use of DOS internals. Once Microsoft actually did this, when it

introduced the IFSFUNC utility in MS-DOS version 4.00. This utility converted

the “dirty” and extremely version-dependent redirector interface into a device-

driver-like interface. However, this utility was removed from MS-DOS versions

5.00 and later (I’ll explain why in a few paragraphs).

Fortunately, the ill-fated IFSFUNC utility was not the only effort to enhance

MS-DOS. In Microsoft Windows versions 3.00 through 3.11, there is a component

called Win386. It has got its name from Windows/386, its ancestor. In early beta

releases of Microsoft’s Chicago operating system this component was called

DOS386. When Chicago was renamed into Windows 95, this component was given

uninteresting name VMM32. Finally, the beta release of Microsoft C/C++ Compiler

version 7.00 included this component from Microsoft Windows under the name

MSDPMI. I think that the best name for this component is DOS386, so I’ll call it

this way.

Probably the reader would ask, “What this component is?” DOS386 is a

multitasking protected-mode operating system. A close inspection of DOS386

reveals that it has almost nothing to do with Windows, and has a lot to do with

DOS (that’s why I prefer the name DOS386 over Win386). Two of DOS386’s

subcomponents, DOSMGR and IFSMGR, are perhaps the heaviest users of DOS

internals. These modules know a lot about the internals of MS-DOS, and they

provide their own interfaces which in fact can help an utility avoid using DOS

internals. For example, let’s return to our SteelBox utility.

This utility needs to access a file from inside an INT 21h call. Most DOS

programmers know that DOS INT 21h API is non-reentrant. It means that no INT 21h

calls can be made while an INT 21h call is already being serviced. Therefore, an

utility like SteelBox would have to play tricks with DOS internals with all the

consequences. On the other hand, DOS386’s IFSMGR subcomponent provides an