Apple logic board 820-3435 at revision B, packaged as a 1.35 MB RAR. Beyond board number and revision the name says nothing, so check the extracted files to see whether a schematic, boardview or both are included. The 820- number is printed on the PCB and the revision letter matters, since component placement can change between revisions. Useful for measuring voltage rails, tracing signals between chips and locating shorted parts on this Apple board.
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.
7-ZipWinRARThe Unarchiver (macOS)