There are three popular types of SD memory card. Normally we can see those cards come with the text labels like SD, SDHC or SDXC. sometimes we see SDSC.

So what are they?

Actually they indicate the card’s storage capacities.

1: SD:

SD actually is Secure Digital. It is earlier age SD card, the default format is FAT16 and capacities range is from 128MB to 2GB.


2: SDHC:

SD High Capacity card.

The default format is FAT32, its capacities range is 4GB to 32GB;


3: SDXC:

SD Extended Capacity card.

The default format is exFAT, its capacities range is 64GB to 2TB.



Since SDXC uses different file system format, so it can NOT be supported by some old devices which were mostly produced before 2010. 

BTW SDSC means SD Stand Card.

About speed:

We also see I, II on SD cards, which means Ultra High Speed Phase I, Phase II on bus design for SDHC and SDXC;

And, we can see the number such as 10, which mean Speed class rating, 2 – 2MB/s minimum peed, 10 – 10MB/s minimum speed;

Also, we could see U1 or U3, which indicate UHS class, class 1 with 10MB/s minimum speed, class 3 with 30MB/s minimum speed;