Greater Performance Choices
There are wide discrepancies in memory card transmission speeds depending on the SD memory card manufacturer and brand. Varying speeds make it difficult to determine which card will provide reliable recording of streaming content. Recording video require a constant minimum write speed to ensure a smooth playback. The SD Association defines various Speed Class standards indicated by speed symbols to help consumers decide what card will provide the required minimum performance for reliability. There are three kinds of speed indications :
Speed Class* , UHS Speed Class** and Video Speed Class*** symbols indicate minimum
writing performance to ensure smooth writing of streaming content such as video shooting. This is important mainly for camcorders, video recorders and other devices with video recording capabilities.
* Seed Class is designed for High Speed Bus IF devices. The Speed Classes defined by the SD Association are Class 2, 4, 6 and 10.
**UHS Speed Class is designed for UHS Bus IF** devices(UHS-I, UHS-II & UHS-III).
The UHS Speed Classes defined by the SD Association are UHS Speed Class 1 (U1) and UHS Speed Class 3 (U3).
***Video Speed Class is designed for both High Speed and UHS Bus IF devices
The Video Speed Classes defined by the SD Association are V6, 10,30,60 and 90.
V6 and V10 are designed for High Speed and UHS Bus IF devices
V30 are designed for UHS Bus IF devices
V60 and V90 are designed for both UHS-II and UHS-III Bus IF devices
SD Speed Class
The host device Speed Class requirements are minimum requirements for optimum performance. If your host device requires a Speed Class 4 SD memory card, you can use Speed Class 4, 6 or 10 SD memory cards. If your host device requires a UHS Speed Class 1 SD memory card, you can use UHS Speed Class 1 or 3 SD memory cards. Video Speed Class is also the same.
Fragmentation and Speed
The memory of a card is divided into minimum memory units. The device writes data onto memory units where no data is already stored. As available memory becomes divided into smaller units through normal use, this leads to an increase in non-linear, or fragmented storage. The amount of fragmentation can reduce write speeds, so faster SD memory card speed standards help compensate for fragmentation.