There is no such thing as a "Windows 98SE" BIOS. The BIOS in a computer is software and data contained on a flash memory chip in a socket on the motherboard. It is provided by the motherboard manufacturer and is specific to your motherboard model and has nothing whatsoever to do with the operating system which is loaded much later on in the boot process. Also it cannot be updated without your knowledge. If you are studying the messages which flash by on your boot up screen, look at the bottom left and you should see the BIOS date.
Clearly 80 conductor cables existed when your BIOS was written, as otherwise the BIOS writer would not have included that message! In fact, 80 wire IDE cables were introduced with the ATA/ATAPI-4 Standard, in guess what year? 1998!
However it's nothing to do with Microsoft, as I explained above.
You could consider getting 80 wire cables, you might see some performance increase.