RAR archive of 866 KB for the Sony VAIO VGN-C22CH on the MS60 platform, tied to the main board number MBX-159. It most probably holds a circuit schematic, which helps with tracing the power sequence, checking for shorted rails and finding test points. A near-identical file exists for MBX-163 on the same model, so read the sticker or silkscreen on the board itself to choose the right one. Where the two revisions differ, component placement and net naming can also differ.
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.