What do memory card classes mean?
What do memory card classes mean?
Memory Cards classes specify the minimum data writing speed that the card is capable of sustaining continuously. These are designations introduced so that the user can select the right media for the application. This is especially the case when recording video or taking still images.
Three main classification systems for Memory Cards
There are three classification categories for SD and microSD cards: Speed Class (C), UHS Speed Class (U) and Video Speed Class (V). Each of these corresponds to different technological requirements and was introduced at a specific time as the needs of users and devices evolved. Speed Class (C) is the oldest system, with designations such as C2, C4, C6 and C10. The number indicates the minimum write speed in megabytes per second (MB/s). For example, C10 guarantees 10MB/s, which is sufficient for basic tasks such as HD video recording. UHS Speed Class (U) is a newer system, designed for higher resolution recording, e.g. Full HD and 4K. It comes in two versions: U1 (10MB/s) and U3 (30MB/s). These classes are used in cards that support Interfaces UHS-I or UHS-II, which significantly increases theoretical data transfer speeds. Video Speed Class (V) is the most advanced standard, dedicated to 4K, 8K, VR cameras and other devices requiring very high and stable transfers. Designations are V6, V10, V30, V60 and V90, where the number also indicates the minimum sustained write speed. The fastest class - V90 - guarantees 90MB/s, which is essential for professional uncompressed video.
Why are memory card classes important?
Contrary to the advertised maximum values, the speed class tells you the real performance of the card under continuous recording conditions, which is crucial e.g. when recording long videos. Using a card that is too slow can result in recording errors, movie freezes or data loss. In practice, this means that a card with a higher class not only provides better performance, but also greater reliability under load, e.g. in continuous shooting mode, recording from surveillance cameras or working with application files on a smartphone. Memory Cards classes are a practical performance indicator that makes it easier to select the right media for specific equipment and type of data work.
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