A Secure Digital card (SD card) is a kind of memory card. Such cards are often used to store images or data in digital cameras. As of 2008, different capacities between 4 Megabytes and 32 gigabytes have been made. The card has a rectangular design, but one edge is chipped off. This means that the cards cannot be inserted into the cameras (or other devices) the wrong way.
There are different kinds of cards:
Those labeled SD, with capacities up to 2 GB
Those labeled SDHC, with capacities between 4GB and 32GB
Those labeled SDXC, with capacities of up to 2 TB (largest made is currently 512GB or 200 GB for MicroSD).
SD and SDHC are not compatible, but devices that accept SDHC also accept SD cards. The interface of SDHC and SDXC cards is the same, but SDXC uses a different file system. Some devices (for example the Wii) that originally shipped only with support for SD can be made to support SDHC with a firmware update.

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