AMIBIOS "Rev-X2-03" (possibly officially called AMIBIOS 2.03) is a version of AMIBIOS, assumed to be made by Access Methods Inc., which then would sell the AMIBIOS code and trademark to American Megatrends. This version is assumed to have been released in 1985 or early 1986.
The only known instance of it is seen on an IBM XT clone motherboard (possibly this model, as the layout is similar), as demonstrated in a YouTube video made by the user Dfgrt924[1]. This is believed to be the earliest known version of AMIBIOS with proof to confirm its existence.
POST screen
The POST screen is visually different from all other known versions of AMIBIOS. It also has two memory test counters (one for base memory and the other for expanded memory) instead of a single merged counter as seen in other versions.
This version also lacks a ROM identification string, with only the copyright and revision being shown where it would usually go. As AMIBIOS 2.2x already had one, the string may have been introduced with that.
It also lacks a setup entrance prompt, which likely indicates it does not contain a built-in setup utility. This may also confirm it was released before 1987 (as the earliest known instances of AMIBIOS with it were released around that time). However, as built-in setups are uncommon on 8088-based ROMs overall (usually even on later ones), this does not certainly indicate such a thing.
Error messages
There are two error messages seen in the video, and they are slightly different compared to the error messages seen on other versions of AMIBIOS.
Floppy drive not ready message:
Drive not ready
Insert diskette in A:
Press any key .....
Floppy drive boot failure message:
Boot failure
Insert diskette in A:
Press any key .....