Compressed archive for the ECS KM400A-M3 motherboard, revision A, sized 681 KB. The name indicates a board built around a VIA KM400A chipset, but it says nothing about the documents included, which are most likely schematic pages. Such material helps when tracing memory and AGP supply rails, locating the clock generator and checking parts near a short on an older desktop board. Unpack it using WinRAR or 7-Zip and compare the board model and revision letter printed on the PCB before working from it.
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.