SDIO protocol is evolved and upgraded from the SD card protocol. In many places, the SD card read-write protocol is
retained. At the same time, the SDIO protocol adds cmd52 and cmd53 commands to the SD card protocol. Because of this, an important difference between SDIO and SD card specifications is the addition of low-speed standard. The target application of low-speed card is to support low-speed I / O capability with minimum hardware expenditure.
MMC is the abbreviation of multimedia card. In essence, it is a memory card specification for solid-state nonvolatile storage , which defines aspects such as card shape, size, capacity, electrical signal, communication protocol between host and so on.
Since the MMC specification was released in 1997, different specifications such as MMC, SD, microSD,SDIO and EMMC have been evolved based on different considerations (physical size, voltage range, number of pins, maximum capacity, data bit width, clock frequency, security characteristics, whether SPI mode is supported, whether DDR mode is supported,
etc.). Although the flowers are charming, their essence remains the same after all, which is why the Linux kernel calls them MMC.
