Firmware dump for the Apple A1989 logic board 820-00850 revision A, packed as a 2.18 MB RAR archive. The name gives a 4MB image, which corresponds to a 32 Mbit SPI flash device on that board. Technicians write such a dump with a programmer when the firmware is damaged or when a locked or corrupted chip prevents booting. Back up the original chip before overwriting it, because it holds machine-specific data such as the serial number. Confirm the 820 board number on the PCB before flashing, since images from other boards will not work.
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 →