Fast memory access between CPU and GPU: The status of Resizable BAR

NVIDIA Resizable BAR

Yesterday, AMD announced the official support of  Resizable BAR for the Ryzen 3000 processors. A week earlier, NVIDIA introduced the GeForce RTX 3060 as the first in-house desktop card that will now support Resizable BAR. We have already carried out initial tests for this.

The requirements for Resizable BAR have been in place for some time but were only used for data center and workstation hardware. The aim is to accelerate access to the ever-larger graphics memory (with some cards we speak of up to 48 GB). AMD had implemented the function as a Smart Access Memory for the current Radeon RX 6000 series and thus cleverly marketed it - so NVIDIA ultimately forced a similar implementation.

But there is currently some confusion as to which combination Resizable BAR works and which does not. And the situation is not that easy to resolve, because there are many dependencies within the platforms.

Resizable BAR at AMD

	Ryzen 5000	Ryzen 3000	Ryzen 1000/2000	10th core generation	11th core generation
	X570, B550, X470, B450	X570, B550, X470, B450	X570, B550, X470, B450	Z490, H470, B460 and H410	Z490, H470, B460 and H410
Radeon RX 6700 XT	✓	✓	✓ *	✓	✓
Radeon RX 6800	✓	✓	✓ *	✓	✓
Radeon RX 6800 XT	✓	✓	✓ *	✓	✓
Radeon RX 6900 XT	✓	✓	✓ *	✓	✓
previous generations of Radeon	✘	✘	✘	✘	✘

✓ *: Different BIOS versions enable Resizable BAR

At AMD, only the current graphics cards of the Radeon RX 6000 series support Resizable BAR. It is not known whether older cards (for example the Radeon RX 5000 series) will still receive support, but it is unlikely. However, all current cards are already able to offer the function via VBIOS and drivers. AMD has now officially announced that in addition to the Ryzen 5000 series, the Ryzen 3000 series will also support Resizable BAR.  According to AMD, a  BIOS with AGESA 1.2.0.1 should be the prerequisite for supporting Resizable BAR with Ryzen 3000 processors. The mainboards can use the X570, X470, B550, and B450 chipset. Some reports confirm it that Resizable BAR also works with Ryzen 2000 processors. However, this depends on the provider of the mainboard and the associated BIOS.

On the Intel processor side, Resizable BAR will only work on the 10th and 11th generation of cores. Most of the mainboard manufacturers of the LGA1200 boards have already published corresponding BIOS updates. Currently, Intel only makes statements about the 400 series chipsets, but Resizable BAR will also work analogously on motherboards with Z590, H470, B560, and H510 chipsets.

Resizable BAR at NVIDIA

	Ryzen 5000	Ryzen 3000	Ryzen 1000/2000	10th core generation	11th core generation
	X570, B550, X470, B450	X570, B550, X470, B450	X570, B550, X470, B450	Z490, H470, B460 and H410	Z490, H470, B460 and H410
GeForce RTX 3060	✓	✘	✘	✓	✓
GeForce RTX 3060 Ti	✓ *	✘	✘	✓ *	✓ *
GeForce RTX 3070	✓ *	✘	✘	✓ *	✓ *
GeForce RTX 3080	✓ *	✘	✘	✓ *	✓ *
GeForce RTX 3090	✓ *	✘	✘	✓ *	✓ *
previous GeForce generations	✘	✘	✘	✘	✘

✓ *: VBIOS update required

So far only the GeForce RTX 3060 supports Resizable BAR on the desktop. The older GeForce generations will probably no longer receive support. All other GeForce RTX 30 cards must first receive an updated VBIOS. NVIDIA plans to release this for its Founders Editions by the end of March. The board partners should also offer corresponding updates.

On the platform side, NVIDIA only supports Resizable BAR for the Ryzen 5000 processors. Anyone who uses a motherboard with an X470 or B450 chipset is of course dependent on the Ryzen 5000 processors working on it. However, there are also reports here that Resizable BAR also works with Ryzen 3000 processors and an NVIDIA GPU - depending on the motherboard and the available BIOS. Officially, however, this is not yet the case.

Anyone using a 10th or 11th generation Intel processor should also benefit from Resizable BAR. With the Comet Lake S models, it should be all processors, on the 11th generation / Rocket Lake S side, NVIDIA and Intel make the cut with the Core i5 models - Core i3 processors are therefore not Resizable BAR support. In terms of mainboards and chipsets, all of the 500 and 400 series can be used.

The first tests with the Radeon RX 6800 XT and Resizable BAR have already shown that not every application benefits from this technology and that it, therefore, depends on which game is used and which resolution is selected here. A similar picture emerged when testing Resizable BAR with the GeForce RTX 3060.

Sooner or later, Resizable BAR will be available for all graphics cards and the current platforms. There is only a negative impact on performance in exceptional cases. The positive effect is currently limited to a few games and while AMD can use all cards of the current Radeon RX 6000 series with it, NVIDIA is still limited to the GeForce RTX 3060. By default, we will include Resizable BAR in the test course as soon as all cards, both from AMD and NVIDIA, are able to do so. As a user, you should definitely try Resizable BAR once, because the increase in performance can be considerable and should be taken with you.