Sometimes the BIOS will just print detected values that also read on the hard drive but can't really understand so big amount of cylinders, it may wrap at some point. Clearly if it would only have NORMAL support it could not perform geometry translation so it will be limited to 1024 cylinders, 16 heads and 64 sectors or 504MB.

But the values you are seeing are quite weird. For DOS it would see the translated geometry where cylinders can be up to 1024 only, and heads can go up to 256 (with limitations).

In LARGE mode, it should multiply heads by two and divide cylinders by two until heads hit the limit (depends on exact type) or cylinders can fit into 1024. So the factor should be 4, as with 3300/4=825 cyls and 16*4=64 heads (and 63 sectors) the hard drive size should still be identical to original, ~1700MB.

It is possible the BIOS understands/stores cylinder values with only up to 2048, as if the hard drive is understood as 2048-16-63 geometry it would have ~1008MB size and after LARGE translation DOS would see 1024-32-63 geometry, same ~1008MB.

Also there seems to be some sort of similar issue with LBA, because the translated logical geometry could have some error by factor of two, because I think the translated geometry should be 825-64-63 as I said above if the whole 3300 cylinders are considered, so consider geometry of 825-32-63, that's about half or ~850MB.

I think one way or another that is a too big hard drive for that BIOS to fully work with it, and there should be no other issues than it having less space available when installed in that system.

In a 486 DOS system, 504MB of NORMAL mode should last some time. LBA would be more compatible if disk is sometimes connected between two computers, but as this 486 has some translation issues another PC might translate LBA differently as well. Perhaps just use the LARGE mode and live with 1GB of storage, and don't try to use the drive in another system. In any event whatever you choose, format the drive with verify or use tool like scandisk to scan the surface as it will try to access all sectors.

Is the drive already partitioned, sometimes that seems to upset translation, if it is already partitioned under another translation scheme.

The values seen are absolutely not weird, but simply some of the other, lesser known BIOS hard disk size limitations in action. You should be able to use the hard disk up to the maximum size indicated by FDISK. LBA or LARGE should work if they are implemented correctly.

Is it not possible to set Bios to normal (504 MB) and use a Disk-Manager (ontrack or from the HDD Manufactur)

I use a Disk-Manager in my Pentium 100 System which have Problem with large HDD.
HDD is now 8.4 GB

Thanks to all ad usual.
I'll trying to set LBA mode and run a scandisk with surface scan.
Btw, yesterday I have switch the drive (IBM 1.7Gb) with
a Fujitsu (2.6Gb): the BIOS detect only 488Mb hard drive but fdisk allow me to
make 2Gb primary partition and 600Mb secondary partition.

Maybe Fujitsu have a better controller? (Anyway, I think to use Fujitsu instead IBM for my 486)

OT: in my childhood I don't remember so much "pain" to build my own pc. It's hard to find
the right item now. 🙁