I managed to find a bios for an IBM 5170 AT 286 Type1 Mainboard. It is here: 30aprile1989 (list here: http://ibm-pc.org/firmware/ibm/5170/5170.htm) In practice I have manually added the number of cylinders, heads, and sect / trk that allow the machine to recognise a disk IBM 250MB. At this point regularly boots DOS. But I wish to program these data permanently in the bios. Does anyone know what program to use and give me the procedure? I tried with BIOSUTL, but the new EPROM do not boot the machine. With BIOSUTL i made what follow: read actual BIOS, you can add new disk geometry parameters at free 47 position, then you have to recalculate bios checsum, then BIOSUTIL devides BIOS into EVEN and ODD file so i can finally program them into two 27256 150nS eprom. Thank you Enrico