Firmware image in .fd format for Apple iMac A1418, logic board 820-00597 revision A, sized 8.00 MB. An .fd file is a raw firmware image and can be written like a .bin in most programmer software. Technicians use it to reflash the SPI chip holding the EFI firmware when the board does not boot or is locked. Back up the original chip first, confirm the board number on the PCB matches, and verify the chip capacity equals the 8 MB image.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @efibios. Enginerys does not host this file.
How to open a .fd file
UEFI flash-device image, typical for Insyde H2O firmware on Acer, HP and Lenovo laptops.
Back up your own chip before writing any dump, and match the full board number and revision. Flashing guide →