Editing SD card (section)

====Command interface====
SD cards and host devices initially communicate through a [[synchronous]] one-bit interface, where the host device provides a clock signal that strobes single bits in and out of the SD card. The host device thereby sends 48-bit commands and receives responses. The card can signal that a response will be delayed, but the host device can abort the dialogue.<ref name="SDHCspec"/>

Through issuing various commands, the host device can:<ref name="SDHCspec"/>
* Determine the type, memory capacity and capabilities of the SD card
* Command the card to use a different voltage, different clock speed, or advanced electrical interface
* Prepare the card to receive a block to write to the flash memory, or read and reply with the contents of a specified block.

The command interface is an extension of the [[MultiMediaCard]] (MMC) interface. SD cards dropped support for some of the commands in the MMC protocol, but added commands related to copy protection. By using only commands supported by both standards until determining the type of card inserted, a host device can accommodate both SD and MMC cards.