I remember several years ago seeing someone with a 2MB SmartMedia card and had their ancient camera connected to the PC with a serial (RS232) lead.
I've two AData 16GB Class 6 Turbo SDHC cards, bought roughly one year apart, the newer shown on the left:
The first scan below is of the older card:
To show that not all card readers are the same, the figures pasted on the right is with this same card in a Sweex internal multi-reader. The main differences seem to be block sizes up to 32KB, especially the 16KB block size.
Now for the scan of the newer card:
While the read speeds are pretty much the same as the first card with the same reader, the write speeds are much slower. I didn't expect this much of a difference, but at least shows something DrageMester mentioned earlier.