Package for the Sony MBX-165 laptop mainboard, carrying MS90 as the project code in parentheses. Sony's MBX designation identifies the board internally, while the MS-style code points to the manufacturer's project naming, likely Foxconn-style, although the name does not confirm the ODM. The 1.34 MB RAR is suited to tracing voltage rails, finding components and diagnosing no-power faults. Extract with any RAR utility and verify that the MBX number on the PCB matches before following the diagrams.
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 @generalschematics. 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.