Modifying 486 motherboards bios

[mob44]

Hallo all,

Iam new here, so let me introduce myself.
My name is Robin and i live in the netherlands. And iam 31 years old.
Why iam here? I having a hobby in the vintage / retro computing.
Iam building old systems from the parts a bought.. When the building is done then iam going to enjoy my systems i really love. My goal is to play the old games on it when we did in 1980 till 2005..

On this part the 486 systems are the most difficult to configure, and sadly most of those boards does have the y2K bug in it.. It also occurs frequently that the support of the processors are very limited.. So there are boards that only will do 486 DX2 66, or having luck when it could reach till DX4 100 mhz. In the years i have been collecting some 486 VLB boards.. And i had have been luck that 2 of those boards supporting the AMD 5x86 P75-133 processors.

There was also a difference that there where boards that could do supporting `write back` processors, and there where board that did only `write through`

I really like to know why was that? Was that only because lack of support from the manufacturer? Or did those boards been unstable with using `Write back`on those boards, so the manufacturer did only choose the save way.

What i also really like to know about that Y2K bug, is this possible to be solved when editting the rom of the bios chip? Because chaintech had always problems on there 486 boards, non of them seems to be working fine.
The boards iam talking about are VLB boards without PCI slots..
I have three boards here that doesnt have that Y2K inside the bios rom.. And i think they came almost from the same release / selling year..
I really like to know how to correct the Y2K bug on those boards.. And i hoping it also could work on some other 386 boards i have..

And is it tough to add more cpu micro code to the rom?
I never had used it before.. I only can tell that i have some cmos chips here, and also an cmos writer / reader.. And i also can clean them in a cmos UV cleaner i have..