First, I am NOT asking how to use the BIOS Setup utility. I'm asking how to OVERRIDE the built-in settings my BIOS Setup supports for the HD geometry.
I have a 1991 NCR PC with a 386SX, on-board IDE, and IBM ROM with "IBM Setup 4.0.0" built-in. As is common for PC BIOS ROM of the era, it offers a fixed table containing the C/H/S (Cylinder/Head/Sector) geometry for 47 different IDE Hard Disk "Types".
None of the 47 HD Types match the geometry of my IDE DOM (Disk on Module), though all of the options are smaller capacity than the DOM.
- fdisk.exe seems to work, creating a partition matching the disk type selected in the BIOS Setup.
- format.exe seems to work, resulting in a volume of the right size.
- copying system files over, or running the MS-DOS installer seems to work for a few drive types.
- BUT, in the end, the written files cannot be read back and the drive cannot be booted.
I suspect if the BIOS C/H/S parameters actually matched the C/H/S parameters of the IDE DOM, then things would work fine. The correct settings are 493/16/63 (it's 242MB).
With all that background, my question is whether there is some way to override the geometry settings that are in the fixed table. I'm imagining I could boot from floppy and use a DOS program to change the CMOS to the right HD parameters. That assumes the CMOS actually stores C/H/S, rather than just the type number from the ROM table.
I suppose if editing the CMOS is not possible or would only be useful to change the type number of the drive, then would it be possible to patch my BIOS ROM to replace one of the existing fixed types with the C/H/S values that I actually require?
NOTE: XT-IDE Option ROM is not a possibility.
Someone will probably suggest XT-IDE ROM extension, but I have not been able to get this machine to recognize it when plugged into an ISA card.