Compressed RAR package, roughly 291 KB, for the ASUS A55BM board in its A variant. The name gives no hint of the contents, but archives of this size tied to a board model usually carry a BIOS image or service documents. Extract it and look at what it actually contains before relying on it. If it is firmware, read and keep the existing SPI flash contents first, then compare the image size with the chip capacity. Make sure the board is really the A version and not the E or another revision, since images for different variants are not interchangeable.
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 @boardview. 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.