Board documentation for Apple 820-2796, packed in a 1.43 MB RAR archive. The name contains only the logic board number, without model, revision or contents. Once extracted, expect a schematic and possibly a boardview usable in tools like OpenBoardView or FlexBV. Apple marks its logic boards with these 820 part numbers, so verify yours first. The drawings are used to trace the power-up sequence, measure rails against expected values and locate components or test points while chasing a fault.
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 @Mac_Shematic_Santale. 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.