And these are the back sides of MMC and SD. You can see SD has two more contacts than MMC and a write protect switch.
Before I had real sockets I used a PCB connector. This only works for MMC, but not for SD. This prototype interfaces a 3.3V MMC to a 5V AVR.
The SD sockets are SMD, but as the pin distance is 0.1" it's
relatively easy to put them on a prototype board. This interfaces
to a STK500 running with 3.3V directly.
And here are the back sides of the MMC and SD sockets. Note that MMCs fit into SD
sockets, but not the other way around.