BIOS image archive for Apple logic board 820-3330, revision B, provided as a ZIP of about 4.2 MB. The name gives no firmware version or model number, so identification rests on the board code, which Apple prints on the PCB. The dump is meant for reprogramming the boot ROM SPI chip with an external programmer when the board fails to boot. Read and save the original contents first, since Apple images carry machine-specific data, and confirm the image size matches the flash 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 .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 →