SD cards have eight pins, while MMC cards have six.
Both multimedia cards (MMC) and secure digital (SD) cards are flash media used to store data. Devices that use MMC and SD cards include digital cameras and MP3 players. Though the two formats are similar, there are a few key differences between them.
History
MMC cards came first, released in 1997 by Siemens AG and SanDisk. SD cards were released in 1999 and were built to nearly the same specifications as MMC so they could be used in devices built to accept MMC cards.
Size
MMC cards measure 24 millimeters (mm) x 32 mm x 1.4 mm. Standard SD cards measure 24 mm --- 32 mm --- 2.1 mm. Mini and micro SD cards also exist for use in devices such as cellular phones and some cameras.
Speed
Where the two formats differ most is in the speed with which they can write, read and access data. As of October 2010, SD cards can transfer data at up to 10 megabytes (MB) per second. MMC cards, on the other hand, can transfer at speeds only up to 2.5 MB per second.
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