RAR archive for the Gigabyte 945GM-DS2 motherboard, revision 2.0, about 1.45 MB, based on the model name built around the Intel 945 chipset family. Contents are not listed, but a schematic is the most likely payload. It can be used to trace the CPU VRM, memory and chipset supplies, check standby circuits and locate faulty components. Before relying on it, read the revision printed on the PCB and confirm it is 2.0, since Gigabyte layouts often change between revisions.
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.