Just to add, Sega Genesis was designed after Master System. Nintendo outsold Sega Genesis in Japan, but it was less successful in the United States. Sega Genesis was sold as the main rival to NEC PC Engine and Nintendo Super Famicom. There also was a slot for ROM cartridges that contained one or multiple games. The unit has 900 games in the library which were a huge deal back in a day and considered as one of the most advanced features in the industry. For the sound, Zilog Z80 was responsible. It is interesting that Sega actually made arcade console smaller and more available and hence Sega Genesis started its life. The console was powered by Motorola 68000 CPU and it was a 16-bit device.
The consoles are identical and they don’t have major differences. Anyway, in the United States and some other countries the console is known as Sega Genesis.
Despite the name, this console was the third version developed by Sega. It became available in the United States in 1989 as Sega Genesis. Sega Genesis started life in 1988 in Japan as Mega Drive.