In 2005 the 4th revision of the MMC standard was releases, which introduced the new MMCmobile as well as the MMCplus.
This was to compete with SD cards as the new standard ran at slightly faster speeds than the current SD card and also much faster than the previous MMC standard.
This new MMC standard is fully backward compatible with the old MMC standard, so an MMCmobile card can be used in a RS-MMC slot (as could an MMCplus card be used in an MMC slot).
The MMCmobile is physically identical to the RS-MMC but faster at up to 52Mhz using an 8 bit wide data bus.
The MMCmobile was primarily introduced however for the mobile phone market, and to make it attractive to mobile phone manufacturers and subsequent content providers so that they’d adopt the format it featured secureMMC, a copyright protection technology. It uses DRM, (Digital Rights Management) similar to MagicGate seen on Sony’s memory sticks.
Therefore its application was pertinent within the mobile phone market, were users would download music from online music stores. DRM provides protection for the copyright holder of the music, so that the end user cannot freely distribute the music they save to their MMCmobile card in their phone.
However, the Secure Digital card had already grasped this market primarily because it was designed with this application in mind from the out set (hence the word “Secure” within its name). Secure Digital features CPRM (Content Protection for Recordable Media), from the very start of it’s existence.
The adoption of such copyright protection by the MultiMediaCard Association in 2005 by introducing MMCplus and MMCmobile to compete with Secure Digital was too late to dominate over Secure Digital, and at the time of writing it looks like MMC is in decline as a choice storage medium for current manufacturers.