Hallo Benny!

 BP> my consern is more or less does it allow to write new bios ? 

I haven't checked.  So far all I have done with it is to bootstrap in a pure
64-bit enviroment and get it to compile the supplied ./examples/hello.bas. 
None of that required any jiggery-pokery with the bios.

 BP> i think its possible not all basic commands that are implemented
 BP> in freebasic ?

I believe the opposite might be true; that more basic commands are implemented
than the garden variety basics, given the different the claim, "You don't need
to learn much new if you are familiar with any Microsoft-BASIC variant.",
posted on the home site https://www.freebasic.net/ as well as the -lang switch
which is worthy of investigation if you are concerned about compatitility.

 BP> i remember only qbasic from my old time when i got a wife 

I never used it even when I had a wife.  I used gwbasic way back when but only
a couple times to suit a onetime solution.  However gwbasic is an interpreter
and not a compiler but I am guessing the syntax is somewhat similar.  That was
30-ish years ago so I can't be sure but I am sure that it wasn't running on a
commodore.

Het leven is goed,
Maurice

... Huil niet om mij, ik heb vi.
--- GNU bash, version 4.4.23(1)-release (x86_64-bonnell-linux-gnu)
 * Origin: Little Mikey's EuroPoint - Ladysmith BC, Canada (2:280/464.113)