Around the school lunch table it was said that the Neo-Geo was 24-bit, even 32. But actually its processor was the Motorolla 68000, the same one used in the Sega Genesis! Only it was clocked twice as fast at 12 mhz, and had a much nicer video chip and more powerful sound.
Actually the Neo Geo was marketed as 24-bit, though it was technically an 8/16/32-bit multiprocessing system. See Wikipedia article: Neo Geo (console)