Gigabyte 945GCM-S2 desktop motherboard archive for revision 3.0, 1.41 MB, for a board based on the Intel 945GC chipset going by the model name. The likely contents are schematic pages showing the VRM phases, DDR2 regulation, the ICH standby rails and the BIOS chip. Technicians use such drawings when a board shows no power, no POST or a short on a supply line. The S2C variant and other revisions are listed separately, so match the exact model and the 3.0 revision on the PCB.
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.