SD cards work in classes - So using even numbers only class 2 is the lowest minimum write speed at 2MB/s and the maximum is 10 been 10MB/s minimum write speed and inbetween you have 4, 6 and 8MB/s minimum write speed
Then you have UHS speed class of 1 and 3 which are the super speed sometimes refered to as U1 and U3 - U3 been the fastest at 30MB/s minimum write speed for use with 4K technology and U1 been 10MB/s minimum write speed - So UHS 3 could read and write at speeds up to around 90 to 95MB/s
In 2012, the CompactFlash Association announced the CFast 2.0 Standard, promising read and write speeds of more than double what was then the current standard. In September 2013, SanDisk released the first CFast 2.0 card, billed as the world's fastest memory card, promising read speeds of up to 450MB/s and write speeds of up to 350MB/s
