NVIDIA ReBAR with AMD, how to activate it on the cards for Ryzen?

Who is going to refuse to win game performance for free and easily? Well surely no one, but that’s what is happening with most current platforms with the new RTX 3000. In this case NVIDIA has been behind AMD, but has reacted quickly and motherboard manufacturers have also moved quickly to provide a large number of models with the ability to move a greater number of textures in less time.

NVIDIA Resizable BAR, where does this technology come from?

As expected by NVIDIA, the BAR technology change was long overdue, but even more so for AMD users, as the company has been selective when it comes to platform prioritization.

Initially, NVIDIA partnered with Intel to release the BIOS updates needed to support this technology, while they themselves released updates for their GPUs through firmware upgrades. But to understand why so many issues and updates, we need to know where this ReBAR technology is coming from.

Rebar or resizable BAR is nothing other than the adaptation by NVIDIA of the BAR technology released with the version PCIe 3.1. BAR stands for Base address register and allows two very specific things via said PCIe bus:

• Specify the amount of memory you want to map a device to main memory.
• After the device is enumerated, it contains the address (base) where the mapped memory block begins.

Depending on the specifications of the PCIe version, a device can have up to six 32-bit BARS or combine two BARs into one 64-bit BAR. But like everything, BAR has a series of questions that need to be clarified to understand how it works:

1. BAR is on the ends. Each endpoint can map up to 6 memory regions.
2. This means that the data received (or to be transmitted) by the PCIe is stored in the memory location specified in the Base Address Register (BAR). If so, why is there more than one BAR?
3. On the one hand, 2 BARS are necessary to achieve a 64-bit BAR (otherwise it is not possible to map this device beyond the 4GB limit), on the other hand, think of a configuration BAR and a Data swap BAR or two BARS for input and one for output.
4. Thus, the memory region that BAR is mapped to is in the device connected to the PCIe (the data is stored in the device’s storage). After allocation, software (eg driver) can read / write device storage through allocated memory region.
5. The memory controller in the processor, the PCIe root complex, and the PCIe device tree will direct memory access to the device rather than main memory.
6. This memory is configured by the PCI device and provides information to the kernel.
7. Each BAR corresponds to a range of addresses which serves as an independent communication channel for the PCI device.
8. The length of each region is defined by the hardware and communicated to the software via the configuration registers.
9. Each region also has other hardware-defined properties in addition to length, specifically the type of memory.

Ultimately, NVIDIA and AMD took the BAR technology and adapted it to their GPUs and drivers, which is why each called it what they saw fit (Resizable Bar for NVIDIA and SAM for AMD). The result is an increase in performance in compatible games as the much commented Gamecaché or RAMcaché is shut down along with the system RAM memory and now the CPU is directly accessible to search for information.

Requirements for ReBAR on any platform

Like everything, NVIDIA sets out some requirements and guidelines that we should follow to ensure that we don’t have any issues on any of the supported platforms:

1. Have a compatible CPU and motherboard (chipset).
2. That we have a compatible BIOS and can enable ReBAR from it.
3. Have a driver equal to or greater than 465.89 WHQL.
4. If we have an RTX 3060 Ti, RTX 3070, RTX 3080, or RTX 3090, we may need to update its BIOS including FE versions. We will know if on our manufacturer’s website the BIOS matches the one that activates ReBAR, the same for higher versions.
5. Once everything is done and we start the PC, we will need to go to the NVIDIA Control Panel to verify that the technology is enabled.

When it comes to processors, motherboards or chipsets, NVIDIA has currently enabled the following:

To all these processors and chipsets we must finally add the Intel Z370 and Z390 platforms, as well as the 8th and 9th generation Intel processors. But what about games? Well, the list at the moment is not too long, but it will be reviewed and new titles will be added.

How can we activate ReBAR if we have an AMD platform?

This was the great doubt of many users, but the reality is that it is activated in exactly the same way as in Intel, in exactly the same way:

We will only have to enter the BIOS, where in our case we have the formula ASUS Maximus X and the X570 E-Gaming to show the examples. If we are in EZ mode, what we will see will be something the same or similar to what is shown in the image above, where in this case we will go to the top and click on resizable BAR.

After that we will see a simple button that will tell us if we want to turn it on or off, we will give it to ON. Another more common method is to go into the boot menu and enable Above 4G decoding, as this is the same setting.

In each motherboard manufacturer it will be different to enable this option, but almost all of them have it clearly visible so that we don’t investigate afterwards, so it shouldn’t cost us too much work. After activating the corresponding option, it remains only to save the BIOS settings by pressing (as a rule) F10 and accepting said save, after which the PC will restart and return to Windows.

There you just need to make sure through the NVIDIA Control Panel that ReBAR is enabled, as shown in the image:

If he says “Yes” then everything went as it should. As we can see, this is a fairly straightforward process that really has more to do with whether we meet the requirements than in the process of activating ReBAR in AMD.