7 SD Card Symbols Explained: What Each One Means

SD, SDHC, and SDXC

SD, SDHC, and SDXC indicate the storage format and capacity range of a memory card. SD cards support up to 2GB, SDHC cards offer 2GB to 32GB, and SDXC cards range from 32GB to 2TB. Check device compatibility before buying a card for your camera or smartphone.

Speed Class: C2, C4, C6, C10

The letter C represents the traditional Speed Class rating, which indicates minimum sustained write speed. C2 supports 2MB/s, C4 supports 4MB/s, C6 supports 6MB/s, and C10 supports 10MB/s. Higher ratings help with recording videos and saving large files, although newer speed standards offer more detailed performance information.

UHS Speed Class: U1 and U3

The U symbol represents Ultra High Speed (UHS) Speed Class ratings. U1 guarantees a minimum sustained write speed of 10MB/s, while U3 guarantees 30MB/s. These ratings matter when recording high-quality video or capturing continuous photos. Your device must support the required UHS interface for the best performance.

UHS Bus Interface: I, II, and III

Roman numerals I, II, and III indicate the UHS bus interface supported by the card. UHS-I reaches theoretical speeds of up to 104MB/s, UHS-II up to 312MB/s, and UHS-III up to 624MB/s. Actual performance depends on the card, reader, and device compatibility, so check specifications before purchasing.

Video Speed Class: V6, V10, V30, V60, V90

The letter V identifies the Video Speed Class, which specifies minimum sustained write speeds for video recording. V30 guarantees 30MB/s, V60 guarantees 60MB/s, and V90 guarantees 90MB/s. These ratings help users select cards for demanding video formats, including high-resolution recording. Always match the card rating to your camera's requirements.

Application Performance Class: A1 and A2

The A1 and A2 symbols indicate Application Performance Class ratings, designed to show how well a card handles app-related tasks. A1 requires at least 1,500 random read IOPS and 500 random write IOPS, while A2 requires 4,000 and 2,000, respectively. A2 benefits depend on compatible devices and card readers.

SD Express: EX or Express Markings

SD Express cards use newer interfaces designed to deliver much higher data transfer speeds than traditional SD cards. Their markings identify support for advanced interfaces, including PCIe and NVMe technology. These cards can help with demanding workloads, but compatibility is essential. Confirm that your device supports SD Express before buying one.

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