Greater Performance Choices
SD Speed Class standards were created to support video recording. SD memory card manufacturers use different types of flash memory to create an SD memory card, so actual transfer speed can vary. Varying speeds make it difficult to determine which card will provide reliable recording of streaming content because recording video requires a constant minimum write speed to ensure a smooth playback. The SD Association defines Speed Class standards indicated by speed symbols to help consumers decide what card will provide the required performance. There are two kinds of speed indications regarding SD bus generation:
Speed Class and UHS Speed Class* symbols indicate minimum video recording performance to ensure smooth video playback. This is important for camcorders, video recorders and other devices with video recording capabilities. The Speed Classes defined by the SD Association are Class 2, 4, 6 and 10.
UHS Speed Class is designed for UHS** devices only and designates minimum writing performance to record video on UHS products. The UHS Speed Classes defined by the SD Association are UHS Speed Class 1 (U1) and UHS Speed Class 3 (U3).
* (Speed Class and the UHS Speed Class are two different speed classes.)
**UHS (Ultra High Speed), the fastest performance category available today, defines bus-interface speeds up to 312 Megabytes per second for greater device performance. It is available on SDXC and SDHC memory cards and devices.