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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
SDIO is like SPI but with 4 data wires instead of 1. Basically all SD cards can also work as Multi-media cards (MMC) - it's an old standard but is easy to use and is open, so it's what we use on Espruino.
As far as I know the higher speed SDIO standard is proprietary - you're supposed to have a license to use it, and I don't believe it is that well documented unless you pay.
Realistically that's what most devices that use SD cards will expect though, so it's what you'd have to implement. Some of ST's microcontroller chips do have an SDIO peripheral on them which you may be able to use (I'm not sure if Espruino's do...), but it'd not something you could do from JavaScript - you'd have to get into some pretty heavy C programming for that.