Does Raspberry Pi 4 support boot medium other than SD card. Can I boot raspberry Pi from EMMC or NOR flash ?
Other than SD card, It is possible to boot Raspberry Pi from USB.
Some Raspberry Pi Compute Module 4 (CM4) boards come with a built-in eMMC flash chip for storing nonvolatile data. This chip replaces the need for a separate SD card, which can be useful if you want to save space on your expansion board or don’t want the user to flash an SD card.