There are four standards for capacity:

SD SD standard – Up to 2GB SD memory card using FAT 12 and 16 file systems
SDHC SDHC standard – over 2GB-32GB SDHC memory card using FAT32 file system
SDXC SDXC standard – over 32GB-2TB SDXC memory card using exFAT file system
SDUC SDUC standard – over 2TB-128TB SDUC memory card using exFAT file system
SD Standard SDHC Standard SDXC Standard SDUC Standard
Capacity up to 2GB more than 2GBup to 32GB more than 32GBup to 2TB more than 2TBup to 128TB
File System FAT 12, 16 FAT 32 exFAT exFAT
SD Logo SD SDHC SDXC SDUC
Form Factor Size SD 32 x 24 x 2.1 mm
microSD 11 x 15 x 1.0 mm

Speed Classes
Normal

Speed

mode

C2, C4, C6
High

Speed

mode

C2, C4, C6, C10,V6, V10
UHS-I

mode

C2, C4, C6, C10U1, U3V6, V10, V30
UHS-II

& III mode

C4, C6, C10U1, U3V6, V10, V30, V60, V90
SD Express mode E150, E300, E450, E600