The SD Association yesterday announced microSD Express, offering the popular PCI Express and NVMe interfaces alongside the legacy microSD interface for backwards compatibility. Like SD Express, microSD Express uses the PCIe interface delivering a maximum data transfer rate of 985MB/s and the NVMe upper layer protocol opens up an advanced memory access mechanism.
MicroSD Express cards defined in the newest SD 7.1 specification will be offered in a variety of capacities such as microSDHC Express, microSDXC Express and microSDUC Express. However, if you’re using an iMac made in 2017 or an iMac Pro, you won’t feel any difference in throughput or speed – at least not when you’re using the Mac’s built-in SD-card reader.
There are no external readers available yet that are capable of handling the new standard, but when the time comes those readers will have to work through the Thunderbolt 3 ports on our iMacs to enjoy the highest throughput speed this standard promises.
As it is now, Apple’s own support page on the subject of its built-in SD-card readers states that an ordinary iMac 2017 only supports the UHS-I standard, with the iMac Pro supporting the UHS-II standard. So, those don’t even support the newest available standard, which is UHS-III and which supports 600+MB/sec throughput.
To be fair, UHS-III isn’t supported yet by any desktop computer I’m aware of, but UHS-II is. To get the UHS-II speed of 312MB/sec, you’ll either need to have an iMac Pro, Satechi’s Type-C USB adapter or a USB-C or Thunderbolt 3 docking station, like the CalDigit TS3+.
These two are capable of reading the second row of PINs UHS-II cards have printed on them to provide for the higher data throughput. UHS-II speed is high enough for quick offloading of high-quality 4K video files, one-by-one, but to enjoy short offloading times when copying multiple 4K video files – ProRes 422(HQ), Raw or uncompressed – we’ll have to wait until UHS-III or microSD Express finds its way into computers. And then, of course, Mac users will need to wait a little longer until Apple decides we can have our cake and eat it too.