Secure Digital eXtended Capacity (SDXC) (2009 – ) | Museum of Obsolete Media (original) (raw)

Secure Digital eXtended Capacity (SDXC) was introduced in 2009 following on from the earlier SD and SDHC formats. SDXC supports theoretical capacities up to 2 TB due to the use of Microsoft’s exFAT file system rather than FAT32 used on SDHC cards. As well as allowing much larger overall capacity, exFAT allows for much larger individual files sizes of up to 4 GB. SDXC cards are designed to be used in devices that require large capacity and fast write speeds such as video cameras or high-end digital still cameras.

SDXC devices are backwards compatible with older SD and SDHC cards, but the transfer speeds will be restricted to the limits of the older cards. However, older devices designed to work with SD cards will not work with SDXC cards, and devices designed for SDHC cards can only use SDXC cards if the card is reformatted to FAT32.

When introduced, SDXC offered bus speeds of up to 104 MB/second if they used the UHS-I (Ultra High Speed) bus standard that was introduced at the same time (and was also made available on SDHC cards). Since then, UHS-II, UHS-III and UHS-Express have increased speeds, and UHS-Express offers speeds up to 985 MB/second. Cards using UHS-II and above have a second row of pins.

SDXC cards also carry one or more speed ratings for maximum write speeds, with three different schemes – Speed Class (ranging from Class 2 to Class 10), UHS Speed Class (1 or 3) and Video Speed Class (V6 to V90). Higher speeds are necessary to support 4K or 8K video and some devices may specify a minimum card speed requirement.

Secure Digital eXtended Capacity (SDXC) (2009 – ) | Museum of Obsolete Media (original) (raw)

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