How compatible were "MS-DOS Compatible" machines?

In the early 8088/86 days, manufacturers like DEC, HP, TI and Zenith thought they could compete with IBM by being "better" in some way. Zenith had 640x400 graphics and did the Tandy 2000. The TI had great graphics. HP, with 3.5" floppy drives, didn't even try to be really try to be compabible - but it ran MS DOS! HP was not even consistent within their own model lines! The HP Portable Plus would not always run programs written for (or ported to) the HP150. When I first became interested in collecting (late 80's) my first target was "DOS Incompatibles" like those named above. I had a Wang PC (great text but little IBM compatibility), Zenith, etc. In the early-mid 80's a program was "well behaved" if it did it's I/O thru DOS calls. Those programs would run on just about anything. dBase II (a port from CP/M) would run on most DOS machines of the time without modification. Mitch Kapor ended that with the release of 1-2-3 and new programs like dBase 3 were IBM PC-specific. A few manufacturers (like HP) paid Lotus to port 1-2-3 to their machine to lure customers but that was a loosing game. So to the original question -- the three requirements will limit the program to "true compatibles", meaning a hardware clone. The most incompatible MS-DOS machine ever, the Seattle Gazelle, uses a serial terminal so the only "sound" available would be the terminal bell. Jim Chris M wrote: