Compressed package for the X450LD motherboard at revision 2.0, stored as a 1.12 MB RAR file. What exactly sits inside is not given in the name, though such archives normally hold repair documentation like schematics or boardview data. Use the extracted files to follow the power-on sequence, check rails at the regulators and locate parts when diagnosing shorts or no-boot faults. Because the same model also appears in revisions 1.1 and 2.1, confirm the revision printed on the PCB before trusting designators or values.
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 @alischematics. 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.