Larger than most in this series, this 11.1 MB ZIP is labelled for MSI board MS-6748. The name names only the brand and model code, so the reason for the size, perhaps several files or a full schematic set, cannot be confirmed without unpacking. MSI marks the MS- number on the PCB, so read it together with the revision before trusting any diagram or dump. Schematics help trace rails and signals, while BIOS images should only be flashed after backing up the existing chip contents.
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 @IT_SERVICE_WORLD. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.