For FAT16, that requires only 4 Gbits, right? There are much more convenient ways of dealing with a 512 kByte memory than SD. So long as an open, complete, and authoritative specification SD isn't published, which it isn't, it's a waste of time using SD, irrespective of how inexpensive they've become.

For small nonvolatile storage, such as what can be handled via FAT16, I'm presently using BBSRAM based on a 256k x 16 10 ns SRAM, but could easily use a similarly sized and pinned-out FRAM, albeit somewhat slower (55 ns). That involves much less overhead and will result in better performance than SD.

What is it about SD/MMC that appeals to you?

RE