Flashing/debugging/running code at external memory in the memory-mapped mode
STM32 microcontrollers have special capabilities running code directly from external flash. To make it possible STM32 made a special set of instructions called memory-mapped mode where the microcontroller is reading instructions from the external flash. Since to read data from an external flash can take some time there is QSPI protocol witch basically four wires used as SPI MISO (Master Input Slave Output) to make throughput 4x time faster than classical SPI. Figure 1 - Illustration of STM32H750 connected to W25Q128JV
