The 64GB Extreme PRO UHS-I microSDXC Memory Card has a capacity of 64GB, is compatible with the UHS-I bus, and features a speed class rating of V30, which guarantees minimum write speeds of 30 MB/s. If your device does not support the V30 standard, this card also supports the U3 standard, which also guarantees minimum write speeds of 30 MB/s. Read speeds are supported up to 170 MB/s, and write speeds max out at 80 MB/s.