The DOS Device Driver Library

Chapter Seven of DOS Internals presents a library named CRTDRVR.LIB that enables the safe use of int 21h functions by DOS device drivers during initialisation. An immediate benefit is that DOS device drivers may be written in C very nearly as ordinary DOS programs. An ordinary DOS program written in Microsoft C typically needs just to be relinked with the CRTDRVR library in order to produce an executable that will still run as a DOS program but which can also be loaded via a device statement in CONFIG.SYS.