AMD Smart Access Memory (PCIe Resizable BAR) Guide

Find out what AMD Smart Access Memory is all about, and how to turn it on for a free boost in performance!

 

Smart Access Memory : PCIe Resizable BAR for AMD!

Smart Access Memory is AMD’s marketing term for their implementation of the PCI Express Resizable BAR (Base Address Registers) capability.

What does that mean exactly?

Well, CPUs are traditionally limited to a 256 MB I/O memory address region for the GPU frame buffer. That means the CPU can only communicate with the GPU through that small 256 MB “window”.

Turning on Resizable BAR or Smart Access Memory removes that small access window, letting the CPU directly access a wider swathe of GPU memory.

AMD Smart Access Memory : How To Enable It?

While the AMD graphics above suggest that Smart Access Memory will widen the memory path (and thus memory bandwidth) between the CPU and GPU, that is not true.

Smart Access Memory / Resizable BAR will not increase memory bandwidth.

What it does is let the CPU directly access more of GPU memory, instead of using the usual 256 MB “window”. That speeds up CPU to GPU communications somewhat.

 

AMD Smart Access Memory : Performance Gains

According to AMD, enabling Smart Access Memory will give you a small but free boost of 5% to 11% in gaming performance.

Here is a summary of the test results from our article, RX 6800 XT Smart Access Memory Performance Comparison!

You can expect up to 16% better performance in some games, but no effect in certain games. But overall, you get a free boost in performance. There is simply no reason not to enable Smart Access Memory.

1080p Resolution (1920 x 1080)

RX 6800 XT Smart Access Memory Performance 1080p

1440p Resolution (2560 x 1440)

RX 6800 XT Smart Access Memory Performance 1440p

2160p Resolution (3840 x 2160)

RX 6800 XT Smart Access Memory Performance 2160p

 

AMD Smart Access Memory : Requirements

Since Smart Access Memory is just an AMD implementation of PCIe Resizable BAR, it can be possibly be implemented for all PCI Express 3.0 and PCI Express 4.0 graphics cards and motherboards.

However, AMD is currently limiting it to a small subset of components, having validated it only for their new Ryzen 5000 series CPUs and Radeon RX 6000 series graphics cards.

So this is what you currently require to enable AMD Smart Access Memory :

Hardware

Software

  • AMD Radeon Software Driver 20.11.2 or newer
  • Latest Motherboard BIOS (AMD AGESA 1.1.0.0 or newer)

AMD currently recommends these X570 motherboards, because they have updated BIOS available :

 

AMD Smart Access Memory : How To Enable It?

If you have all of those supported components above, and updated your motherboard BIOS, you need to manually enable Smart Access Memory.

Now, the method will vary from motherboard to motherboard, and it probably won’t even be called Smart Access Memory.

Instead, look for variations of Above 4G Decoding, or Resizing BAR, or Resizable BAR.

In our guide, we are using the ASUS CROSSHAIR VIII Hero (AMD X570) motherboard, as an example :

  1. First you will need to turn off CSM (Compatibility Support Module), or make sure it’s disabled.Go to the Boot menu and look for a CSM / Compatibility Support Module option.

  1. Set CSM (Compatibility Support Module) to Disabled.

  1. Go to the Advanced menu and look for the PCI Subsystem. In other motherboards, look for PCIe / PCI Express configuration options.

How to enable AMD Smart Access Memory

  1. Enable Above 4G Decoding.

How to enable AMD Smart Access Memory

  1. This will give you access to the Re-Size BAR Support option. Set it to Auto.

How to enable AMD Smart Access Memory

  1. Now go to the Exit menu, and select Save Changes & Reset.

  1. It will ask you to confirm the changes. Just verify both, and click OK.

After the motherboard reboots, AMD Smart Access Memory (PCIe Resizable BAR) will be enabled for your Ryzen 5000 series CPU and Radeon RX 6000 series graphics card!

 

CSM Warning For GIGABYTE AORUS X570 Master

AMD currently recommends these X570 motherboards, because they have updated BIOS available :

CSM is disabled by default for the ASUS, ASRock and MSI motherboards. However, it is enabled by default in the GIGABYTE AORUS X570 Master.

If you installed Windows without first turning CSM off, it will be configured as non-UEFI. It will NOT boot if you enable Resizable BAR Support (Smart Access Memory).

You will need to reinstall Windows with CSM support disabled.

 

Recommended Reading

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