Overview
In 1989, Sega decided to enter the next generation of console gaming with a 16-bit machine. Compared to the main competition - the NES - this new machine, named the Mega Drive, was incredible. Vibrant colours and fast-paced gameplay meant near arcade-perfect conversions of Sega's hits were available in homes for the first time.

The machine was launched across the world under its original name, the Mega Drive, except in North America. Over there, it was re-christened the "Genesis", although was essentially the same machine under the hood.

Models
As with the Master System, there were three versions of the Mega Drive/Genesis released. All software released was compatible with all models, as were the upgrades - so a Mega Drive II could be used with either a Mega-CD (Sega-CD in the US) or a Mega-CD II (Guess.) With each model, the physical size of the machine dropped, so that by the time the Mega Drive III was released, it was tiny compared to the original machine.

Technical Specifications
CPU: A 16-bit Motorola 68000 processor running at 7.67 MHz.
RAM: 64K Internal Memory, 64K Video Memory
Screen Resolution: 320 x 224

Maximum on-screen colours:
64 on-screen, 512 total
Sound Channels: 6, all FM Stereo

Accessories
Control Pad: Originally, the system was released with a 3-button controller (there was also a seperate Start button). As time went on, and people saw the wonder that was the SNES controller, Sega released a new 6-button controller. This was compatible with just about all the 3-button games, and some games were released which could only be played with a 6-button. Even with games that didn't require it, it soon became a necessity for some (most notably fighting games like the Street Fighter II series).
Power Base Converter: Because the sound was handled by a Z80 processor (the same as the CPU used in the Master System), the Mega Drive was physically capable of running Master System code. Sega saw this and released the "Power Base Converter", which allowed one to use a Master System cartridge on the Mega Drive.
Menacer: With every games console released, a new lightgun follows. The Menacer was more of a bazooka to the Master System's pistol-like Light Phaser. The Menacer required a base station to be plugged into the controller port, and was a solid, reliable gun. It was only compatible with its own software; Konami's unofficial game was incompatible.