Bill of materials archive for the ASUS A8S, a 123 KB RAR; the BOM token in the name indicates a parts list rather than a schematic. A BOM links each reference designator to its part number, value and package, which is handy when choosing an exact replacement for a burnt MOSFET, capacitor or IC, or checking an unreadable marking. It is usually a spreadsheet or text document openable in an office program. No revision is stated, so check that the parts listed match those fitted on your 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 @schematicslaptop. 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.