The Sega Card or Sega My Card media format was an alternative to cartridges, designed by Sega for use with the SG-1000, Sega Mark III and Sega Master System. The latter two used cards with the name Sega My Card Mark III in Japan, to differentiate them from those designed for SG-1000 hardware.
Sega Cards were typically cheaper to produce, but have a limited storage capacity of 32KB. The idea at the time was to distribute bigger games on cartridge to be sold at a higher price, while smaller games would be distributed on card at a reduced price. Sega backed both formats during the 1980s, but phased out the Sega Card format in 1989 due to limited popularity with consumers. It was also considered a health risk, with younger children trying to eat them.
In Europe the majority of games distributed on card were re-released on cartridge (the exception being Great Soccer, which had already been discontinued since being superseded by World Soccer). However, the US card games failed to see a cartridge re-release, whilst the Sega Master System had already been discontinued in Japan by this point.
Unlike Master System cartridges which are of a completely different shape in non-Asian regions, both Western and Asian Sega Cards are physically identical. However, as Asian SG-1000 and Mark III games generally lack a ROM header (which the bios of Western systems require) Asian Sega Cards are not compatible with Western Master Systems. Systems without a card reader (the original SG-1000, SC-3000, and redesigned Sega Master System II) can use the Card Catcher to run card-based games. The Power Base Converter was the last piece of hardware to contain a card slot, however, as the Sega Mega Drive cannot run SG-1000 games, the slot is restricted solely to Mark III/Master System cards.
The Sega AI Computer also ran Sega cards, though they were incompatible with other systems.