Good news: The SD Association has added yet another confusing specification layer to SD cards.
The new "UC" spec extends the maximum capacity of either a full-size or micro SD card from 2TB to 128TB. And the "Express" spec increases the peak transfer speed of a full-size card from 624MB per second to 985MB per second.
That, in theory, puts SD in a better position to use high-bandwidth file types such as 4K and 8K video, as well as for expansion in small devices.
All of which means that the SDA's incomprehensible matrix of SD's "consumer-friendly" labeling now looks like this:
The new card specification is based on the UHS-II/III SD card design -- the one with the extra row of connectors. It's backwardly compatible with any reader that can take those cards.
It also uses a new architecture based on the PCIe Gen3 and NVMe controllers in larger devices, which may mean it will be a while before cameras and other small capture devices can take advantage of it. Even some recent cameras that offer two SD card slots still only offer one that takes advantage of UHS-II.
You're also unlikely to see 128TB capacities for a while -- the maximum of 2TB was introduced in 2009, and no one ever released a product at that capacity. In 2016, SanDisk announced a 1TB card, but it never seemed to ship. The current maximum available from anyone is still 512GB. Plus, the slower (peak 95MB per second transfer rates) pro-level 512GB cards cost around $200, which means even a 2TB card would be expensive. And a 2TB Express card would be obscenely expensive. A 128TB Express card would probably cost more than a car.
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The new card specs might be promising for storage expansion in laptops, where it's impractical at best (and impossible at worst) to swap in larger storage and the faster speed would come in handy.
985MB per second (7.9Gbps) is much lower than USB-C 3.1's peak of 40Gb per second, but most reasonably priced external drives claim about 10GB/sec, which is still faster. So an external drive will likely be more cost effective for a while. And built-in SD card readers also tend to be the cheapest possible, which means they're unlikely to support the new standard for a loooong time as well.
Plus, smaller devices such as detachable laptops, tablets and phones, as well as drone cameras and action cameras have moved on to micro SD. Despite the previous theoretical 2TB maximum, micro SD only made it to 512GB this year, and we're just starting to see mainstream card manufacturers start to offer them in that capacity.
So hope for, but don't expect to see, these capabilities.
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Here's a 400GB microSD card It doesn't come cheap though