Sony MS90 project archive for motherboard MBX-165, revision 1.0, roughly 1.30 MB in RAR form. The contents are probably schematic pages for this VAIO board, read in a PDF viewer. MS codes are Sony internal project names, and the MBX number is printed on the PCB itself. Technicians use such drawings to trace power rails, follow the power-on sequence and locate components or test points around a fault. Verify that MBX-165 and revision 1.0 match your board before measuring.
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.