In the NodeMCU v3 specs it says it has 4Mb flash memory. In the ESP-12EX datasheet it says the MCU has no rom, but can boot from an SPI external memory.
However, I don't see any flash memory chip on the board, so I was wondering... where is it ?
It's covered by the can/shield.
On the picture below, the shield is removed. The IC in the right of the ESP is the flash.