Firmware dump for the Apple iMac A1418 with logic board 820-01237, revision A, compressed into a 4.76 MB RAR. The 820- prefix is Apple's own logic board numbering, so the number and revision printed on the PCB should match before you flash anything. Images like this are used to restore a corrupted boot ROM by writing the SPI flash with an external programmer. Read and keep the original chip contents first, since they hold serial and machine-specific data, and confirm the image size fits the chip.
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 @biosarchive. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
Back up your own chip before writing any dump, and match the full board number and revision. Flashing guide →