ASUS Z370/Z390 board owners are furious over the lack of Resizable BAR support [Update]

A visual representation of how PCIe Resizable BAR works

The PCIe Resizable BAR (ReBAR) feature was first introduced by AMD last year dubbed as 'Smart Access Memory' and since then rivals Intel and Nvidia have also added support for it. Various graphics card AIBs and motherboard vendors have also been gradually rolling out firmware updates to enable the feature. ASUS motherboard owners however are annoyed because the company hasn't yet released any such BIOS to add support for ReBAR on its older high-end Z390 and Z370 chipsets even though others like MSI and Gigabyte are doing so.

In December last year, a thread was started on the ASUS Republic of Gamers (ROG) Official Forum to inquire about ReBAR support on Z390 and Z370 chipsets, and needless to say, after four months of inactivity from ASUS, they are not too happy as nothing has materialized so far. Below is a response from a seemingly loyal ASUS motherboard owner who is annoyed at the negligence from ASUS:

You know what, the fact that ASUS hasn't even commented in here to give any update as to whether they will be supporting this or not is kind of ridiculous. I have been a loyal Asus customer for many years. I upgrade my rigs on an extremely regular basis, in the last 4 years I've had an Asus z170 board, x99 board, x299 board and now z390 board.

Here's another response from a different user:

I still cannot actually believe Asus have not responded in here.

You are shameful Asus, Treating your 9th gen users like this who have spent extra for your so called premium boards and you are completely silent on the matter

Another poster seems more patient about the situation but would still appreciate some response:

I don't mind waiting as there were bugs in the bios releases from other vendors. What most of us are angry about is the complete silence. Just release something. Let us know, hey guys, you need to upgrade to a 4 series.

There has never been any official announcement that it is in the works for the 300 series. Just a random forum admin post is not confirmation. The lack of mention in their actual official press release is what causes concern and their lack of transparency.

While some seem to have given up on the company entirely, like this commenter below:

Regardless of whether ASUS launches the Bios update for the RESIZE BAR, this was my last Asus product, I will never buy any type of product from ASUS again.
It is no longer the first time asus has done this type of thing, and the most serious of all is not even responding to its customers.
Oh and just to finish I was very stupid in 20 years to have used products all of them from ASUS.
Goodbye ASUS

While the company hasn't officially communicated anything regarding the matter yet, in some of the responses to these posters outside of the thread, it may have hinted that some work may be going on for adding ReBAR support on the last-gen Intel Z-series chipsets. It could possibly be encountering stability issues on such boards in its current state when the ReBAR support is enabled. However, only ASUS knows the real reason for this omission.

The PCIe Resizable BAR function allows the CPU to have full access to the entire memory of the GPU, whereas typically a processor can only address 256MB for compatibility with 32-bit OSes. As a result, thanks to the entire VRAM now being available, requests from the CPU can be performed in parallel instead of sequentially, which in turn improves the speed of their dispatch. It's claimed to be especially helpful nowadays since game assets keep getting bigger.

And although the performance differentials in games today aren't very significant, it could certainly change in the future when titles are better optimized to take advantage of the PCIe ReBAR funcion. So it's easy to see why these ASUS owners are angry at the firm considering how expensive the Z-series chipset boards are, as well as 34 pages (so far) with no official response.

Source: ROG Forum

Update: An admin on the ROG Forum has responded after we posted the article. According to him, the company is working on adding the PCIe Resizable BAR support to ASUS Z390 and Z370 chipset motherboards and the expected rollout of the feature is between late April and early May.

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