NVRAM
There’s a IS25WP256 SPI NOR flash chip on the board, connected through QSPI0. In Linux it appears as:
mtdblock0 31:0 0 32M 0 disk
It’s not used by default (it came filled with 0xff here), but it can be used for boot. See Booting from Flash - #3 by drmpeg .
firmware
The only built-in firmware is the ZSBL (Zero-Stage BootLoader) in ROM 0x00001000-0x00001FFF and 0x00010000-0x00017FFF. It’s mask ROM so cannot be replaced. It loads the second stage from another device, either the flash or SD card.
persistant RAM that do not erase with shutdown
There’s also OTP, which is, as the name implies, one-time programmable. AFAIK by default it is only used for the serial number.
As for details how to access these, refer to the FU740-C000 manual.