RAR archive of 320 KB titled M5A78L_USB3, matching the ASUS M5A78L USB3 motherboard name. The content type is not indicated, so after unpacking determine whether it is a board layout, circuit diagram or firmware dump. Layout files open in viewers such as OpenBoardView and are used to locate parts, follow nets and measure at test points, while firmware needs an SPI programmer. Confirm the exact model and revision on the PCB, since several M5A78L variants exist with different layouts.
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 @boardview. 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.