pcper said:

NVIDIAs performance labs continue to work away at finding examples of this occurring and the consensus seems to be something in the 4-6% range. A GTX 970 without this memory pool division would run 4-6% faster than the GTX 970s selling today in high memory utilization scenarios. Obviously this is something we cant accurately test though  we dont have the ability to run a GTX 970 without a disabled L2/ROP cluster like NVIDIA can. All we can do is compare the difference in performance between a reference GTX 980 and a reference GTX 970 and measure the differences as best we can, and that is our goal for this week.



Accessing that 500MB of memory on its own is slower. Accessing that 500MB as part of the 4GB total slows things down by 4-6%, at least according to NVIDIA. So now the difficult question: did NVIDIA lie to us?



At the very least, the company did not fully disclose the missing L2 and ROP partition on the GTX 970, even if it was due to miscommunication internally. The question should the GTX 970 be called a 3.5GB card? is more of a philosophical debate. There is 4GB of physical memory on the card and you can definitely access all 4GB of when the game and operating system determine it is necessary. But 1/8th of that memory can only be accessed in a slower manner than the other 7/8th, even if that 1/8th is 4x faster than system memory over PCI Express. NVIDIA claims that the architecture is working exactly as intended and that with competent OS heuristics the performance difference should be negligible in real-world gaming scenarios.



The performance of the GTX 970 is what the performance is. This information is incredibly interesting and warrants some debate, but at the end of the day, my recommendations for the GTX 970 really wont change at all.

The configurability of the Maxwell architecture allowed NVIDIA to make this choice. Had the GeForce GTX 970 been built on the Kepler architecture, the company would have had to disable the entire L2/MC block on the right hand side, resulting in a 192-bit memory bus and a 3GB frame buffer. GM204 allows NVIDIA to expand that to a 256-bit 3.5GB/0.5GB memory configuration and offers performance advantages, obviously.



Lets be clear  the performance of the GTX 970 is what the performance is. This information is incredibly interesting and warrants some debate, but at the end of the day, my recommendations for the GTX 970 really wont change at all. It still offers incredible performance for your dollar and is able to run at 4K in my experience and testing. Yes, there might in fact be specific instances where performance drops are more severe because of this memory hierarchy design, but I dont think it changes the outlook for the card as a whole.



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For users that are attempting to measure the impact of this issue you should be aware that in some cases the software you are using report the in-use graphics memory could be wrong. Some applications are only aware of the first "pool" of memory and may only ever show up to 3.5GB in use for a game. Other applications, including MSI Afterburner as an example, do properly report total memory usage of up to 4GB. Because of the unique allocation of memory in the system, the OS and driver and monitoring application may not always be on the page. Many users, like bootski over at NeoGAF have done a job of compiling examples where the memory issue occurs, so look around for the right tools to use to test your own GTX 970. (Side note: we are going to try to do some of our own testing this afternoon.)



NVIDIA has come clean; all that remains is the response from consumers to take hold. For those of you that read this and remain affronted by NVIDIA calling the GeForce GTX 970 a 4GB card without equivocation: I get it. But I also respectfully disagree. Should NVIDIA have been more upfront about the changes this GPU brought compared to the GTX 980? Absolutely and emphatically. But does this change the stance or position of the GTX 970 in the world of discrete PC graphics? I dont think it does.