Important: The following only applies to RPi5 with 8GB RAM!
The SDRAM_BANKLOW=1 boot option is default in newer EEPROM versions since rpi-eeprom v2025.01.22-2712 and it works very well, gives a nice boost in performace.
It may be set manually in eeprom-config to be sure.
Please do not try hacks with older bootloaders.
PS: See the version of the bootloader eeprom via terminal:
vcgencmd bootloader_version
Update to the latest eeprom via terminal:
raspi-config
Then select update this tool or similar (wording changes now and then) and let run.
Restart raspi-config, look for something like bootloader version (can be inside advanced) then latest-something. Ok. Let reboot. Recheck.
In Terminal to edit boot eeprom config:
sudo -E rpi-eeprom-config --edit
A good and fast one is:
[all]
SDRAM_BANKLOW=1
HDMI_DELAY=0
BOOT_UART=0
NET_INSTALL_AT_POWER_ON=0
NET_INSTALL_ENABLED=0
USB_MSD_DISCOVER_TIMEOUT=1000
BOOT_ORDER=0xf164
POWER_OFF_ON_HALT=1
CTRL-s to save, CTRL-x to exit. This gives the option to boot a USB stick to make repairs or to play something else, without noticable delay when booting other memory devices, then boots NVMe and then µSD, all without big delay. Overall it is the fastest boot config possible nowadays. If it makes problems with NVMe or super-slow USB drive, just leave it blank and set the boot order inside raspi-config.