MMCmicro is a smaller format factor MultiMediaCard (MMC), even smaller than the Reduced-Size MultiMediaCard (RS-MMC) which already significantly reduced the size of the MMC card. An MMCmicro card has typical dimensions of 14mm x 12mm x 1.1mm, compared to RS-MMC's dimensions of 24mm x 18mm x 1.4mm. MMCmicro supports dual voltage, just like MMCmobile and can be used in full size MultiMediaCard and Secure Digital slots with the aid of a mechanical adapter.
MMCmicro support the 4x features including high speed data transfer and 4-bit bus features (but falls short of 8-bit because it doesn't have the extra pins required.) While it looks remarkably like a microSD card, it is important to point out that they are not compatible in any way.
MMC products also are marketed in a variety of different brands.
RS-MMC --> Stands for Reduced-Size MultiMediaCard, introduced in 2004 with a smaller form factor.
DV-MMC --> Stands for Dual-Voltage MultiMediaCard, a substantial change to MMC that introduced dual-voltage cards.
MMCplus --> Introduced in 2005, MMCplus runs at higher speeds. Also marketed as "MMCmobile".
MMCmobile --> Introduced in 2005, MMCmobile runs at higher speeds. Also marketed as "MMCplus".
MultiMediaCard --> Original MultiMediaCard format.
miCard --> Introduced in 2007, this version of the card technically has a maximum capacity of 2 Terabytes (2TB).
SecureMMC --> SecureMMC is to provide a secure removable storage to secure applications using as MMC card.