What is the difference between secure digital (SD) and SmartMedia?

[figgypower]

This might be an incredibly stupid question, but... I'm kind of confused over Secure Digital cards and SmartMedia cards. I guess what confuses me is they look similar to me and the names sound alike. Are Secure Digital cards "secure" versions of SmartMedia cards? If SD cards are the "secure" version of SmartMedia cards, what does that mean? Do they encrypt data, or what? Or... am I just confusing myself for no reason and they're just entirely different media forms?

Also, my Sharp Zaurus 5500 is said to support Secure Digital / Multimedia Card (MMC) - I guess that's what's kinda confused me... Is MMC yet another media? Is MMC a type of SD? I appreciate the responses to clear up my confusion...

 

[figgypower]

Nevermind, finally found a FAQ on digital cameras that explained the different medias. If anyone else is curious, you can check out the digital camera faq. Mods, if you see this - no point in this post I guess and you can just delete it.