You've probably been seeing those glowing articles about how fast and large in storage those SD cards are going to get in the "next" generation, called SD Express.
This is a media campaign, and it seems to have hit plenty of targets, most of whom are just re-writing the press release because they have nothing else to write about in the photographic world at the moment.
Let me point a few things out.
We still don't have consumer UHS-III cards yet in the wild, though that specification has been available for awhile (February 2017). Now we suddenly have the following generation of cards being promoted.
What we're seeing is a public relations campaign by the SD Association to dull (the already available XQD and) CFExpress card momentum before it gets going. "See, we can do PCIe, too." is what the latest press release and new white paper are all about. "And ours goes to 11" (128TB).
Let's start with that last bit. Get the highest density chip you can find from a chipmaker at the moment and stick it in the space that an SD allows. Is that 128TB? Not a chance. Not even close. And the white paper wants you to believe that this will show up in microSD cards, too ;~).
While I haven't seen one myself, you can probably cram 1 or 2TB today into the allowable space using current technologies (the largest I've seen is 512GB, though in a microSD card, so 1-2TB seems about right). And as another site pointed out, even at those promised 985MB/s speeds—still not an eighth of what CFExpress will do—it would weeks to transfer 128TB anyway, so I'm not exactly sure why I'd want it.
But what strikes me is that UHS-I fallback. If your device doesn't do SD Express, the speed is going to drop from 985MB/s to a max of 104MB/s, the UHS-I maximum. In other words, the new standard won't be backwards compatible with the previous two standards it replaces (UHS-II and UHS-III). (Press release: "These innovations maintain the SDA’s commitment to backward compatibility." Technically accurate, but misleading, as the Express part takes over the UHS-II and UHS-III pins with no compatibility, leaving only the original pinouts compatible.)
No wonder Apple decided to get rid of SD card slots on computers.
As if to make matters worse, the SD Association has approved new marking standards that will just add more confusion to the already confusing ones they have. You might see a card labeled SDHC EX I, for example. Wait, I just pulled a current UHS-II card from my camera and it's labeled SDHC II. So I is better than II, now? It is if it's your EX ;~).
Meanwhile we still have camera makers using card slots that can't even max out UHS-II speeds (and some adding mismatched SD card slots that perform at different speeds, including that soon to be fallback slower UHS-I 104MB/s).
Look. I'm for progress, and I know it will come. I wouldn't mind having a pair of UHS-III slots in a camera and cards that performed at 624MB/s. But I don't. About the fastest I've encountered is the Sony A9 at about 152MB/s on only one of its two card slots. That's half the claimed speed of UHS-II, by the way.
So just go ahead and let your mind slip into the future past the point where we get actual 312MB/s UHS-II cards, let alone 625MB/s UHS-III cards, and let it contemplate a future with 128TB 985MB/s SD Express cards. What is that, eight years from now, best case?
Both the CompactFlash Association (CFA) and SD Association (SDA) are currently waging "future design win" wars using press releases in lieu of actual product. Ignore them. Unless, of course, you're developing a device that uses removable cards, in which case you might want to try to figure who's doing what when and why.
Note that the CFA's press release on CFexpress was almost two years ago (Oct 2016). We've got a few prototype products floating around now, but nothing mainstream that I've yet seen. So check back around the time of the Tokyo Summer Olympics. Maybe we'll see something then.
