An extra-fast memory card format currently used only in the Nikon pro DSLRs. It’s about half the size of Compact Flash but has the potential for extremely high speeds – though it’s yet to be seen whether many other camera makers will adopt it.
UHS is a new ultra high speed bus (data transfer connection) for SD memory cards. There are two versions: UHS-I and a more advanced UHS-II type. This refers to the physical construction of the card and does not directly indicate its speed. There are speed standards for UHS cards: UHS 1 guarantees a minimum speed of 10MB/s, which is suitable for full HD video recording, and UHS 3 guarantees a minimum transfer speed of 30MB/s, which is what you’d need for 4K video.
These are all the same size but there are important differences. Older cameras may only be able to use SD cards, but more recent ones will be able to use SDHC cards too, but may not be able to use the latest SDXC format. Check your camera’s manual before buying these.
Memory card makers quote the card’s maximum read/write speed in MB/sec, but it’s also important to know the minimum sustained speed for video recording. This is quoted using Class ratings (SD cards). Typically, you need Class 10 for 4K video as a minimum.
This is measured in gigabytes (GB), and the larger the memory capacity the more photos and video clips you can store. It’s hard to give precise advice since cameras and user needs vary so much, but 16GB is a good starting point if you shoot RAW files as well as JPEGs, and consider 64GB-256GB if you want to shoot video, especially 4K.