Apple logic board firmware for board number 820-2577, revision A, provided as a 2.64 MB RAR. The name gives no model, so identify the machine from the 820 number printed on the logic board. Apple uses the 820-xxxx pattern for its own board part numbers. Such a dump is normally written to the SPI flash with a programmer to recover a board stuck by corrupted firmware. Back up the original chip first, since it holds machine-specific data like the serial number, and check the chip capacity against the image size.
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 →