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So the dithering was done because the 9801 could only display 16 out of 4096 colors, and only the 9821 or models with Window Accelerators could do 256. To properly program the system you had to know color theory.
The sound system on the other hand is a similar chip to the Neo-Geo and it shows for the 9801-86 card, while the 9801-26k was a YM2203. Both feature FM channels and PSG/SSG channels from the YM2149 (think Atari ST) giving it a distinct sound system. Drivers existed to also mutliplex the PCM channel meaning that many games used the PCM channel with multiple sampled sounds at once (on top of it having several PCM drum samples in the chip's ROM).