The Sega My Card was a ROM card for several models of Sega video game console, initially released in Japan in 1985 as a cheaper means of game distribution than cartridges.
The original My Card was for use on the Sega SG-1000 game console (and SC-3000 computer), where it needed an optional accessory called the Card Catcher as they were released before the My Card was released.
A second version was labled as the My Card Mark III and was for use on the Japan-only Sega Mark III console released in 1985. By 1986, Sega began to move to cartridges as the primary format and by 1987 had stopped releasing games on the My Card Mark III format. The Sega Mark III can read the original My Card version.
Outside of Japan, there was a third version released in 1986 and marketed as the Sega Card for use on the Sega Master System, the international version of the Mark III.
The My Card and My Card Mark III had a limited capacity of up to 32 KB.