Is there any difference between machine language written for PC-DOS 2.0 and machine language written for PC-DOS 2.1?
PC-DOS 2.1 was introduced with the PCjr. It has exactly the same features as version 2.0, but works on all IBM PC-series computers. DOS 2.0 is recommended only for the PC, PC-XT, and Portable PC. There should be no significant differences in machine language programs written for either DOS, especially if the programmer intends to keep the software compatible with all computers in the IBM PC family.