RAR archive of about 1.13 MB for the MSI B85M-G43 micro-ATX motherboard, board MS-7823 revision 1.2, based on the Intel B85 chipset named in the model. The contents are not listed in the name, so expect schematic or boardview data and check after extraction. Technicians use such material to follow the CPU core and memory power rails, examine the standby and power-on circuitry and find test points. Revisions of the same MS-number can differ, so make sure the PCB marking shows 1.2 before relying on the layout.
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 .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.