Resizable BAR (Base Address Register), which can boost throughput between a CPU and a GPU to improve performance, isn't some type of alien technology from another universe. In fact, the feature has been part of the PCIe specification since Revision 2.0. Still, it has gone under everyone's radar until AMD brought it up in the mold of the chipmaker's Smart Access Memory (SAM), with the caveat that it would only work if you paired a Radeon 6000 series GPU with a Ryzen 5000 CPU and X570 motherboard. The Red Team certainly spearheaded the adoption of Resizable BAR, and now Intel and Nvidia are working to bring the technology to their corresponding products.
ASCII's testbed included a Core i9-10900K (Comet Lake-S) processor, Asus ROG Maximus XII Extreme on the latest 1002 firmware, and a Radeon RX 6800 XT (Big Navi) graphics card. Enabling the Resizable BAR feature was easy and only required enabling the "Above 4G Decoding" and "Re-Size BAR Support" options in the motherboard's BIOS. ASCII performed its tests across four modern titles: Assassin's Creed Valhalla, Forza Horizon 4, Red Dead Redemption 2, and Tom Clancy's Rainbow Six Siege. The publication used the highest image quality for each game at a 1920 x 1080 resolution.
Resizable Bar On Intel Z490 Benchmarks
On Assassin's Creed Valhalla, Resizable BAR improved the minimum and average frame rates by 12.8% and 14.2%, respectively. In Forza Horizon 4, we're looking at 20.3% higher minimum and 19.4% average frame rates at 1920 x 1080, and 17% better minimum and 15.9% average frame rates at 2560 x 1440.
As for Red Dead Redemption 2, activating Resizable Bar netted improved minimum and average frame rates up to 181.6% and 7.8%, respectively. The explanation behind the massive improvement in minimum frame rates is that the game's benchmark tends to suffer from dips during the run. However, Resizable Bar seems to resolve that issue, which explains the improved values.
The overall takeaway from ASCII's testing is that Resizable BAR has a significant impact on gaming performance in titles that support the feature. As noted, not every game engine benefits from Resizable BAR. For example, Resizable BAR has a negligible effect on average frame rates in Tom Clancy's Rainbow Six Siege, although it did improve minimum frame rates by 11.8%.
In the midst of all the impressive numbers, we have to bear in mind that the 1002 firmware from Asus is currently in the beta stage, and the performance uplift with Resizable BAR enabled is evidently visible. It'll be very interesting to see whether the final firmware improves performance even further.