How does Resizable BAR work?

Resizable BAR is a technology that is being talked about a lot lately, and it is that with it you can gain an extra graphic performance without having to spend a single additional euro . First of all, it must be said that both AMD and NVIDIA use this technology, only that AMD has ended up calling it Smart Access Memory (AMD SAM). This technology is based on making a shortcut for the information that goes from the graphics to the CPU, so that a direct bus is used and the data arrives much earlier than without it.

Although Resizable BAR is already referenced in the PCIe specification since version 2.0, it has not been until now that it has begun to take advantage of it. The PCIe 3.0 version added numerous changes to the technology and laid the foundation for what it is today.

Some time ago we learned about the implementation of Resizable BAR in both NVIDIA and AMD , but it was not until a few months later that it could not be tested in a good way. But before continuing, let’s see what Resizable BAR is specifically about and how it works.

How does Resizable BAR work?

Resizable Base Address Register , which is the full name, is based on using the PCIe bus for communications between the VRAM chips of the graphics and the CPU. Without Resizable BAR, these communications between VRAM and CPU are made through a 256 MB data buffer , which implies that from the graph they go to this bus, fill up and then go to the CPU, including additional latencies that are noticed with high graphic load.

With Resizable BAR, it is possible to modify the capacity of said buffer , ensuring that communication is completely fluid, since the 16-line PCIe 4.0 bus (typical of graphics cards) has a bandwidth of 31.5 GB / s. And not only that, Resizable BAR also allows parallel communication, so that several buffers of a certain capacity can be used simultaneously.

This implies that a graphic with 32 GB of VRAM can download all its information in a single second to the CPU. In real environments, in demanding games with changing screens and new information everywhere, this is a significant advantage, especially going forward when there are more demanding games. The image generated by the GPU at every moment must be quickly retransmitted to the CPU so that it interprets it and can appear on the screen, which is imperceptible to us given how fast it happens.

If we have an open world game for example, with a newly loaded 4 GB screen (for example), without Resizable BAR the graphics memory would have to perform 16 full iterations with the CPU, since the buffer limit is 256 MB.

If we move around the world a bit, some areas will quickly begin to render and others to disappear from the screen, which implies that the appropriate data must be modified, which will easily exceed those 256 MB of limitation. With Resizable BAR, this problem is solved in one go, since it makes it possible to make this space in the buffer more dynamic, in addition to enabling simultaneous paths when working in parallel.

This is a clear advantage in practically all games, with those with fast and changing screens such as car and action games benefiting the most . The increase in FPS is evident, then we will see some examples.

How to activate Resizable BAR

The implementation of the Resizable BAR technology must be done at different levels. GPU, GPU drivers, CPU, motherboard and operating system must be compatible . This is due to the fact that a modification of the communications between CPU and GPU is carried out at a low level, which affects many components and requires additional implementations in drivers and instructions by the CPU.

By NVIDIA, this technology is called as is, Resizable BAR, while AMD has called it AMD Smart Access Memory, but they are based on the same PCIe specification. There are basically three possible configurations for its implementation:

  • NVIDIA GPU + Intel CPU

We note that AMD’s configuration with Intel is not supported. This is because specific instructions are required from the processor, which AMD has worked extensively on to make them compatible with its graphics cards. Since NVIDIA does not manufacture CPUs, it has had to open its range to both Intel and AMD options and work with both companies for this implementation.

In addition to these possible options, there is also the Intel + Intel , which will happen when the manufacturer launches the Intel Arc Alchemist graphics , and we can already predict that they will incorporate Resizable BAR.

Components Compatible with Resizable BAR

With this data in mind, only a few models from each manufacturer are compatible with the technology:

  • NVIDIA GPU: Any of the GeForce RTX 3000 series
  • AMD GPU: Any of the Radeon RX 6000 series
  • Intel CPU: All of the 11th Gen except the Core i3, plus all of the 10th Gen
  • AMD CPU: All of the Ryzen 5000 series (Zen 3), in addition to the Ryzen 3000 except the Ryzen 5 3400G and Ryzen 3 3200G
  • Intel chipset: Any of the Intel 500 series, plus the Intel Z490, H470, B460 and H410
  • AMD chipset: Any of the AMD 500 series, in addition to those with Zen 3 compatibility in the AMD 400 series (with AMD AGESA BIOS or higher)
  • NVIDIA Drivers: From GeForce Game Ready 465.89 WHQL
  • AMD Drivers: From Radeon 20.11.2

As we can see, with NVIDIA RTX 3000 and AMD Radeon 6000 graphics , Resizable BAR can be implemented without limitations regarding the range occupied by the graphics in question.

To activate Resizable BAR, you must enter the BIOS and look for the option, which is usually in the advanced configuration or advanced menu sections. It may appear under the name Re-Size BAR Support . From AMD they indicate that it is also necessary to activate the Above 4G Decoding option .

Compatible games

Not all games can benefit from Resizable BAR first. We must first differentiate between NVIDIA’s proposal and AMD’s, since both are applied separately and somewhat differently. NVIDIA’s, which is called by the same name as the technology itself, requires certain checks and tests on your part, while AMD’s applies to all existing games.

In this way, NVIDIA Resizable BAR acts on a limited list of games, while AMD SAM works on all titles . It is true that both AMD and NVIDIA specialize their drivers so that they become compatible with certain games as they come out, and that they offer optimizations for this new technology. That is why it is expected that there will be a noticeable increase in the list of games supported by NVIDIA over time.

NVIDIA Resizable Bar Compatible Games

  • Assassin’s Creed Valhalla
  • Battlefield v
  • Borderlands 3
  • Control
  • Cyberpunk 2077
  • Death stranding
  • DIRT 5
  • F1 2020
  • Forza Horizon 4
  • Gears 5
  • Godfall
  • Hitman 2
  • Hitman 3
  • Horizon zero dawn
  • Metro Exodus
  • Red Dead Redemption 2
  • Watch Dogs Legion

You will find more information about this updated list from NVIDIA’s own drivers.

How many FPS do we gain with Resizable Bar?

As we mentioned before, the results with this activated technology are noticeable. The profit is there, it may not be a great leap for certain games, but it is something that you get for free , if you buy the right components, of course. Official NVIDIA data points to a 12% improvement under an RTX 3080 , while AMD’s data points to a 15% improvement, based on various settings.

NVIDIA Official Data

In reality, things change quite a bit. These test equipment many times do not reflect reality, since they are controlled and calculated environments so that the increase in performance is the maximum possible and thus be able to give this data to the media.

AMD official data

For our part, we have not been able to test NVIDIA Resizable BAR or AMD SAM with enough titles to draw conclusions, so we are going to refer to some other world-renowned media such as Techpowerup and PCWorld.

From Techpowerup we can see that NVIDIA Resizable BAR achieves around a 3-4% improvement in the games that are supported, while those that are not on the official list get a 1-2% improvement at most.

On the part of PCWorld we can see tests with both AMD SAM, but only with the top-of-the-range graphics, the RX 6900 XT . In this case , an average 5% improvement is observed with the games tested, highlighting some cases such as Borderlands 3 at 1440p that achieves an increase of 8.4%.

The actual data is not comparable to the advertised. That both technologies are an improvement is obvious, the percentages are there, but they are not as much as advertised. At the moment it remains to wait a while for new games to be incorporated by NVIDIA and for the drivers to be optimized by both .

Resizable BAR supposes improvement of FPS and is totally free

As we have said in the previous section, both NVIDIA Resizable BAR and AMD SAM are technologies that improve FPS in games without having to spend additional money. They have really lax performance requirements – they require latest and penultimate generation components, but they are not limited to top-of-the-line components . This implies that the mid-range configurations are greatly improved, since they are usually the most economically attractive for users. As we saw in the corresponding section, all NVIDIA RTX 3000 series graphics are compatible, as is the case with AMD Radeon 6000 series .

You can expect a somewhat higher performance improvement over a long list of games, which will happen over time . Something that will also happen over the years is that the games will ask for more resources and the graphics will have more memory, which will cause the size of the Resizable BAR buffer to increase. This is not a problem, since each new version of PCIe doubles the available bandwidth, so it goes accordingly. As the technology is implemented, it is possible to have this buffer of up to 256 GB, so there are many years until this can be a problem, since the buffer without Resizable BAR is only 256 MB and does not have a large performance impact currently.


by Abdullah Sam
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