First there was a MMC card which was used in older Nokia phones. It was too large so they reduced its size by half and thus formed the RS MMC which was the reduced size MMC. This card can be used in devices which support MMC with an adaptor. Then came DV RS MMC which was the dual voltage variant. This can run at a lower voltage than standard RS MMC in devices which support this card, consuming less battery power. It is also backward compatible. This card is different from microSD, miniSD, SD, Memory Stick etc.