On 486 machine:

When booting from floppy drive, it detects cd-rom drive properly.

When booting from Seagate 80GB drive that is formatted as 8GB, it won't detect cd-rom drive in both Windows 98 and DOS (using VIDECDD.SYS).

NSSI shows CD-Rom, so BIOS detects it.

Any clues why this happens? When I boot from floppy, or boot from second 4GB drive, cd-rom is present even this Seagate 80GB is also present as slave. Only when booting from Seagate 80GB, cd-rom is not detected.