The Rise of SD Cards
Next on the block were SD cards. SD stands for secure digital, and these cards quickly rose to the top of the memory heap due to their high capacities and improved speeds. In the beginning, however, a standard SD card could only handle a capacity of 128MB to 2GB. Standard SD cards are a rare breed these days, as the industry has moved on to SDHC and SDXC cards. The file format for SD cards was FAT16, originally. They can be used in any device that has an SD card slot.
So what are SDHC and SDXC? SDHC cards use a different file system, FAT32, which can handle capacities between 4GB and 32GB. SDXC cards use exFAT, and support capacities between 64GB and 2TB, though 2TB cards aren’t on the market yet. Hardware-wise, there are no differences between SDHC and SDXC cards; however, older SDHC card readers that aren’t able to understand the newer exFAT file format won’t read SDXC cards. SDXC-compatible card readers and cameras will always be backward compatible with SDHC and normal SD cards reader, though.
Traditionally, SD cards were always a few steps behind CompactFlash cards when it came to performance, but since CompactFlash cards haven’t been updated in a while, SD cards have recently passed them with UHS-II cards. UHS-II SD cards offer read speeds up to 312 MB/s, almost twice the speed of UDMA 7 CompactFlash cards. However, because they are so new, not many cameras and card readers support UHS-II cards, and while UHS-II cards are backward compatible, they won’t work at full speed with older card readers. In fact, most high-end DSLR cameras are still unable to write at UHS-II speeds.
microSD cards are essentially just miniaturized versions of full-size SD cards, and share all the same classifications. Like their full-size brethren, there are microSDHC and microSDXC cards; there are even UHS-II microSD cards, and they have the same speed-class ratings. However, due to their small size, they typically are a little slower and available in lower capacities than the top-of-the-line, full-size SD cards.
But do you need that much storage?
It depends. A 4GB SD card can hold about 280 RAW images and 1,500 high-quality JPEGs. A 128GB card would be a nightmare to manage, with almost 9,000 RAW images and 48,000 high-quality JPEGs. Many photographers prefer smaller-capacity cards that can be easily labeled and managed.
For non-photographers, adding SD memory can be a blessing, especially if your device is low on internal memory. Many tablets, for instance, ship with low internal memory (and is mostly used by the system software and internal processes) and having an extra slot to increase memory could mean the difference between watching a lot of HD movies and being stuck with low-res home video of your sister’s Sweet 16 birthday party.