Sega SC-3000H: An updated version with more RAM and keyboard (the original keyboard was of the low-end membrane type).
Sega Master System: Essentially the same as the Mark III only with a different name and a few minor adjustments
Sega Master System II: An update to the Master System with a new smaller redesigned frame, as well as inbuilt game "Alex the Kidd in Miracle World.
Sega Mega Drive: Known as the Sega Genesis in North America due to another company owning the Mega Drive trademark in that region.
Sega Mega-CD: Known simply as the Sega CD for the North American market, it allowed CD based games as well as Audio CDs to be played on the Mega Drive.
Sega 32X: Hardware update to the Mega Drive allowing 32-bit based games to be played
Sega Multi-Mega: a portable CD player with the functionalities of a Sega Mega Drive and Sega Mega CD. Following the Mega ... brands, its name was Multi-Mega in most of the world and Genesis CDX in North America.
Amstrad Mega PC: Although not actually produced by Sega themselves, the Mega PC is Amstrad's version of the TeraDrive for European and Australian markets, thus includes electronics for Sega's Mega Drive console built-in.