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
.pcb	.pcb board file	FlexBV or the viewer it was exported from
.rar	RAR archive	7-Zip or WinRAR
.bin	BIOS image inside the archive (usually .bin)	a CH341A, XGecu T48 / TL866II Plus or RT809H programmer