SDIO is fast and SPI is slow. However, the SDIO of STM32 is not easy to use, especially the 4BIT mode, and the 1BIT mode can be used, and the speed is about 2M bytes per second.
With SPI is relatively stable, the speed is between 1-2M bytes per second, which is suitable for cases where the speed is not high.
SPI is an acronym for Serial Peripheral Interface. SPI, is a high-speed, full-duplex, synchronous communication bus, and only occupies four wires on the pin of the chip, saving the pin of the chip, while saving space for the layout of the PCB, providing convenience, it is out of this simple and easy to use characteristics, now more and more chips integrate this communication protocol, such as AT91RM9200. SDIO defines a peripheral interface on the SD standard. Currently, SDIO has two main categories of applications - mobile and non-mobile.
Removable devices are available as extensions to Palm and Windows Mobile to add Bluetooth, camera, GPS, and 802.11b capabilities.
Non-removable devices follow the same electrical standards, but are not required to meet physical standards.
Some phones contain an 802.11 chip that connects to the CPU through the SDIO. Such a move would be... Precious " The I\/ O pin resources are used for more important functions.