I've used all the above. 2.13 was the earliest one I used. UCDOS is an improvement on it, and CCDOS97 is the culmination. I still have the CDOS that came with CAD R12 (compressed to less than 10K), the very standard source code and programs of CHCS Chinese character system by the author of CCDOS97. I also developed a ZWxs display module myself, which supports direct screen writing, doesn't occupy the system clock, takes less than 2K in size and memory each, and the internal code supports GB, GBK, BIG5, Beida 748, etc. It doesn't include Western table recognition and input method, and displays 15X16 character patterns. I'm not a computer major, but I'm good at English. That's all my capabilities. If someone can add to and improve it and then make it available for everyone to use, I'm welcome. Don't laugh at me!
my major is english----my love is dos----my teacher is the buddha----my friends--how about U