Originally posted by: npoe1
What is the difference and which one do you prefer?
CompactFlash Type II Card Slot (3.3v)
Secure Digital / SDIO Now / MMC Memory Card Slot
I like CompactFlash, but at 5 volt signaling. The reason is 3.3 volt signaling always struck me as 5 volt's annoying little brother. When I started tinkering with electronics, I first ran across 5 volts, and 5 volts just has a nice ring to it, nice and angular. On the other hand, 3.3 volts sounds a little too round and bumpy. I have already gone through enough glue logic to interface 3.3 volt devices with 5 volts to want to keep things simple and level. CompactFlash is nice and can be more or less transparently ATA compatable. I use CompactFlash (with 5 volt signaling!) for my solid state Linux server.
Admittedly, MMC/SD cards can be accessed with SPI, which can be convenient too. I much prefer MMC over Secure Digital, something about the simplicity and open standards. I have never programmed with the ATA bus directly, and I have much more experience with SPI, so I guess if this was on a microcontroller forum, I would of chosen MMC/SD. However, this is a computer hardware forum, and I find CompactFlash cards more convenient in this context.
On a slightly broader note, I think the gradual shrinking of flash card sizes is silly. I hold nothing against CompactFlash cards because of their relatively large size, and I detest the xD cards. Flash memory is small enough already, and I don't see a need to force the point.