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Difference Between SD and MMC Flash Cards

Flash memory is a basic necessity of any electronic device these days.  Today we will talk about MultiMedia Cards [MMC] and Secure Digital [SD] cards. First, a bit of history.  The MMC format was developed by SanDisk and Siemens back in 1997.  SD media was developed, jointly, by SanDisk, Panasonic and Toshiba.  The SD standard was developed to improve upon the MMC format. The two memory card types look the same.  They are both about 24mm x 32mm x 2.1mm in size, or about the size of a US postage stamp.  The one obvious, physical difference between the two is the Lock/Unlock switch on the left side of SD media.  MMC does not have a sliding switch.  The switch is meant for users to put the media into a Write Protected state.  A condition where the user could read from the card, but could not write to it, or delete content off it. The other physical difference between MMC and SD media is on the bottom side of the flash card.  The MMC has 7 copper connectors and SD had 9 copper connectors.  MMCPlus has 14 connectors on it.  For a more technical reason please read here. The MMC media has a transfer rate of around 9MB/s.  The SD media is much faster with write speeds of 10MB/s and higher [always improving]. Both MMC media and SD media, are for the most part, interchangeable when being used in electronic devices.  Of course it is always best to check with the manufacturer of your device, but it’s a general rull of thumb, both are interchangeable.  With MMC media, it is more likely a customized piece of hardware, like GPS or medical equipment will require the MMC format, where-as most MP3 players, cameras, and “retail” electronics will take both types.

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