The SD standard is owned by San Disk and they require you to pay them to be allowed to make a card. They will allow you to make a NON UHS reader free but to call it SDXC if it's not USB or fireware or other universal interface then as part of the standard it is required the OS support EXFAT witch requires a license from MS. At least that's my understanding and the information I'm working from is several years old.
Sorry, but that is both misleading and very wrong. Although SanDisk WAS one of the original companies that pooled together to create the Secure Digital Association. However, it is a non-profit with 1000+ members. Although not 'Free', the SD standards are at least 'Open' though not 'open source'.
ExFat drivers have been available on the Pandora for several years and I would be shocked if they don't get built into the OS for the Pyra. Yes, ExFat IS a Microsoft thing. There are now ExFat Linux drivers, but Microsoft was not much help in getting there. Yes, these cards can all be re-formatted to whatever your heart desires.
Anyway, there are several things going on with SD (and eMMC) control for the Pyra. To my understanding for the Pyra...
eMMC is limited to about 208 MB/s (Bus limit)
Internal microSD is limited to about 104 MB/s (Bus limit & Max UHS-I speed)
The two exposed SD slots work off of a different system and I've never fully understood what is controling them. However I'm under the assumption that they run at the same 104 MB/s theoretical maximum bus rate.
Official SDXC logo
The Secure Digital eXtended Capacity (SDXC) format, announced in January 2009 and defined in version 3.01 of the SD specification, supports cards up to 2 TB (2048 GB), compared to a limit of 32 GB for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's exFAT
file system as a mandatory feature.
Version 3.0 also introduced the Ultra High Speed (UHS) bus
for both SDHC and SDXC cards, with interface speeds from 50 MByte/s to 104 MByte/s for four-bit UHS-I bus.
Version 4.0, introduced in June 2011, allows speeds of 156 MByte/s to 312 MByte/s over the four-lane (two differential lanes) UHS-II bus, which requires an additional row of physical pins.
Version 5.0 was announced in February 2016 at CP+ 2106, and added "Video Speed Class" ratings to handle higher resolution video formats like 8K
The new speed ratings go up to 90 MB/s.
I'm looking forward to when we can benchmark different SD and uSD cards on actual Pyras to find out what works best. That was entertaining on the Pandora - until a few years in when we got to a time when all commercially available cards were already faster than the Pandora could go.
Hopefully someone will port over an HDD/SSD performance graphical benchmarking suite so we can have a standard measure to use other than entering dd commands.