Resizable BAR mod for older motherboards

Hi Guys,
I am completely new to this forum, so please don’t blast me if this question is ignorant. I thought if I could ask it anywhere, it possibly would fit in here.

To what I have been reading, any PCI Gen3 compliant board can technically support resizable BAR, but I don’t suppose that motherboard manufacturers will introduce Resizable BAR to older PCI Gen3 motherboards. So, I was wondering if this could be something can be modified in as a customization.

Looking forward to your thoughts.

I test some motherboards with z97 chip set and only few of them have the code above 4g decoding witch needed to enable re-sizable bar.
The code for resizable bar dont exist so it cant be modded.

Thanks for the prompt response @boombastik , I am glad that some smart people have already looked into it. I have ASUS Z97 Sabertooth Mark2. Do you think it is possible to enable re-sizable bar on that board?

EDIT: So I did some digging, and it looks like I have Above 4G decoding option on the board, I have enabled it now.

So, what should be our next step.

You edit the BIOS, or you see this option then you go in your start menu?
Keep in mind that with above 4g need csm mode off and pci legacy slots will not work.

I saw this ‘Above 4G’ option in the BIOS without any modding. It was in the BIOS menu next to CSM. CSM is disabled in my BIOS yes.

So, should we mod for RBAR now? Or what should we do next in your opinion.

It cant be modded because the code is not there at least is not possible for me.

OK. I misunderstood. I thought that if code for ‘above 4G decoding’ exists then we can mod.

Is it possible to inject this code from Z490 BIOS down into the Z97 bios? They both support above 4g decoding. Not sure what else would be a dependency there.

Following…gotta be away to get this to work on older boards. I also have above 4G decoding in bios, but resize bar is not enabled.

Certainly looking forward to it. Looks like even though Haswell is able to address entire 64Bit space in BAR, it still needs to negotiate how much memory can GPU claim as IO Region.

Resizable BAR working on Ivy Bridge CPU and motherboard from 2012 : pcmasterrace (

This thread seems interesting, the OP seems to have figured out how to get Resizable Bar working on an intel ivy bridge system…

Its here also on the forum… not that i beleieve in this at all, smells cosmetic and useless to be honest, despites the user effort and respect for his achievements.
A non supported chipset and gpu…

[Experimental] Resizable BAR DXE driver - BIOS/UEFI Modding / BIOS modules (PCI ROM, EFI and others) - Win-Raid Forum (

There are successful results

Thats a Z170 and a RX 6900 XT and RTX 3090 (RBAR cards…), not RX580 and Z75…lol