Transfer speeds up to 200mb/s [requires a compatible device capable of reaching such speeds, such as the sandisk sd uhs-i card reader.performance depends on host device, interface, usage conditions and other factors. 1mb=1,000,000 bytes.X= 150kb/sec perfect for shooting 4k uhd video(1) and sequential burst mode photography(1)full hd (1920x1080) and 4k uhd (3840 x2160) video support may vary based upon host device, file attributes and other factors capture uninterrupted video with uhs speed class 3 (u3) and video speed class 30 (v30)(2). (2)uhs speed class 3 designates a performance option designed to support 4k uhd video recording with enabled uhs host devices. Uhs video speed class 30 (v30), sustained video capture rate of 30mb/s, designates a performance option designed to support real-time video recording with uhs enabled host devices.