BIOS (EFI firmware) dump for the Apple iMac A1418, EMC 2638, logic board 820-3588-A. Apple's 820-xxxx numbers identify logic boards, and the suffix letter marks the revision. A1418 is the 21.5 inch iMac. The 4.15 MB ZIP is used to rewrite the SPI boot ROM when the machine fails to chime or start after firmware corruption. Back up the original ROM first, since it contains the serial number and other unit data, and confirm the board number and the flash capacity before writing.
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 .zip file
Compressed archive that every operating system opens without extra software.
Back up your own chip before writing any dump, and match the full board number and revision. Flashing guide →