Region coding

A common region lock screen denoting a game designed only for NTSC-J Mega Drive systems.

More than any other Sega system, the Sega Mega Drive is affected by differing forms of region coding, implemented so that games were optimised for (or locked out of) three main marketing regions; NTSC-J (Japan and parts of Asia), NTSC-U (North America) and PAL (Europe and Australia).

Like the Sega Master System and rival console the Nintendo Entertainment System, Japanese cartridges are a different physical shape to their Western counterparts, meaning Japanese games could not be played on American systems or vice versa without some sort of adapter (or by disassambling cartridges or consoles). However, Mega Drive hardware is also configured to be one of the three aforementioned regions, meaning software could adjust itself depending on what sort of Mega Drive system is detected.

The latter is not an unusual practice (and indeed similar methods were employed for many consoles going forward), however unlike more modern systems, software was under no obligation to adapt to the detected region, meaning only part of the Mega Drive's game library takes note of what type of system is in use.

For information, see Mega Drive region coding.