SD vs. MMC: Which card is for you?

Security
Since SD stands for "Secure Digital", it doesn't take much for one to know that another major difference between an SD card and MMC is security. While the MMC has no security features, SD cards have a built-in security element that allows cryptographic security for copyrighted data. This means you won't be able to copy information or applications that are pre-installed on a card and pass this on to other users. This feature is most useful to companies which decide to distribute data on SD cards as this will prevent someone from copying applications or information and using it on another card or device.

The security level of the SD card also complies with requirements set by the Secure Digital Music Initiative (SDMI), a forum that brings together folks in the recording, consumer electronics, and information technology industries to develop technology specifications for protected digital music distribution. Hence, music files can be distributed without the worry of being copied to another device.

The SD card also has a write protect switch on the case. Similar to your floppy disks, you can manually protect your files from being modified or overwritten by flipping the catch found on the card.

The security features on the SD card is actually most useful for those who intend to sell cards with content since your data and software cannot be copied illegally. But for a user who wants to use the SD card for storage or even run apps off the card, the additional security features are not really useful. Also, the copyright protection feature takes up about 100K on your card, meaning that you've less storage space to work with.

Similarly, the write protect feature seems to be quite redundant since you'll need to read and write to the card frequently anyway. So unless you absolutely want the security features, the MMC is sufficient.