A BIOS dump is a full image of the board's SPI flash chip. It is written back with an SPI programmer when the original firmware is corrupted, after a chip replacement, or to recover from a failed update. Read and save the original chip first: serial number, DMI data and the Intel ME / AMD PSP state differ between boards.

Tools to open these files

Format	What it is	Open with
.rar	RAR archive	7-Zip or WinRAR
.rom	raw BIOS ROM image	a CH341A, XGecu or RT809H programmer