Maximum Read Speed This is the maximum read speed of the card usually given in Megabytes per second (MB/s). Note that cards rarely are able to sustain these speeds for long periods of time.
This is another (rather outdated) way of expressing the max read speed. It is based on the read speed of audio CDs at 150 KB/s. You can figure out how fast a 1000x card is in KB/s by multiplying 150 by 1,000 and converting KB/s to MB/s by dividing by 1,000 (the answer is 150 MB/s). You could also just go by a card’s stated 150 MB/s speed, in figure 2.
Type This is the type of card; different card types use different file formats and newer cards won’t work in older card readers.
UHS Speed Class Rating This is the minimum sustained writing speed of the card; important for video recording. UHS Speed class 3 cards will never write slower than 30 MB/s, UHS Speed class 1 cards never slower than 10 MB/s.
Speed-Class Rating This is an older speed-class rating. It is redundant of the UHS speed class, but many card manufacturers include it, as well, since many consumer products still recommend products based on the old standard. A class 10 is the fastet of the old speed class ratings and a class 10 card is verified to never write slower than 10 MB/s, class 4 would be never slower than 4 MB/s.
UHS Rating The UHS rating of a card determines the maximum bus speed at which a card can read, assuming the memory in the card is fast enough to match it. Non-UHS cards max out at 25 MB/s, while UHS-I cards support up to 104 MB/s, and UHS-II cards support up to 312 MB/s. Both the card reader and card must support the same standard to benefit from the increased speeds, but UHS cards are backward compatible with older readers—they just won’t be as fast in them.
Capacity This is the card’s capacity: SD cards range up to 2GB, SDHC cards range from 2GB to 32GB, and SDXC cards range from 32GB to 2TB.