Despite its performance benefits only being realized in the past several years, resizable BAR has been readily available as part of the PCIe specification for decades now. Even so, many older Intel and AMD motherboards don’t formally support the feature, with compatibility put ultimately out of reach by a lack of manufacturer support via UEFI updates. Not content with this reality, one modder hopes to change this.
If you’ve used one of the best gaming CPUs of the last four years to build a gaming PC, namely anything more recent than an AMD Ryzen 5000 or 10th gen Intel Core chip, you’re likely already living with the advantages of resizable BAR (or Smart Access Memory as AMD calls it). There will be some variance depending on your motherboard chipset, but if you’re using anything older than the aforementioned processors, this mod could help push your GPU performance further.
Modder xCuri0 has created a custom UEFI DXE driver, dubbed ‘ReBarUEFI’, that, “enable[s] Resizable BAR on systems which don’t support it officially.” Now, it’s important to clarify that this doesn’t work for every motherboard out there, but the number of reported working boards thus far is impressive.
To give a brief explanation of why resizable BAR is potentially so beneficial to older systems, you’re essentially removing a bottleneck between your CPU and GPU in their ability to communicate. Without the feature, your processor can only access your graphics card’s frame buffer in 256MB chunks, but Resizable BAR makes it possible to access the whole lot, which considering VRAM allocations can be upwards of 20GB, is quite the difference. This can result in performance increases and is absolutely necessary for Intel Arc GPUs to work well.
Comments from users who have tried ReBarUEFI indicate that this mod works with Intel processors that are over ten years old, along with now aging Zen 3 Ryzen chips.
Suffice to say, there’s little harm in trying this mod for yourself if you have an older system that you’re hoping to squeeze a little more out of. You’ll find the list of working motherboards as well as details of how to install ReBarUEFI over on xCurio0’s Github, as well as a list of known working motherboards.