GTX 970: what was the slower memory issue all about?

magellan · Sep 22, 2015

I read somewhere that the GTX 970 used to have slower access to the last 500MiB or so of memory. I've also read that this isn't the first time Nvidia has done something like this (i.e. slowed memory access for some percentage of the total memory of a GPU). I can see why they might do it (so the GTX 970 doesn't perform like the GTX 980).

So, is the rumor true? Why did Nvidia hamstring the GTX 970? How did they manage to slow the access to certain addresses in the memory VRAM but not others? If a game does end up using the slowed memory does it make a significant difference in FPS or frame-time latency?

dejo · Sep 22, 2015

the ram isnt really slower, it just works slower as its on a narrower bus width. but 3.5gb will run at 7/8 speed and .5gb will run at 1/8 speed if it the card is using more than the first 3.5gb

NiHaoMike · Sep 22, 2015

Something about the memory addressing, akin to (but due to a different mechanism) the "3.5GB" issue that affected PCs back when 64 bit was just coming to the consumer market.

It does make for a very dramatic drop in performance, if your game or other performance critical app happens to use the last 512MB. I actually did a test.

If you open Facebook or other image heavy site and scroll through a bunch of pictures to fill up part of the VRAM (modern browsers cache decompressed images in VRAM to accelerate scrolling) and then start a game so that it crosses the addressing "barrier", you'll find the game unplayable. But if you first open the game, pause it, open Facebook and scroll through a bunch of pictures until the VRAM is almost completely full, you can resume playing the game with basically no performance impact!

Bishoff · Sep 25, 2015

magellan said:
I read somewhere that the GTX 970 used to have slower access to the last 500MiB or so of memory. I've also read that this isn't the first time Nvidia has done something like this (i.e. slowed memory access for some percentage of the total memory of a GPU). I can see why they might do it (so the GTX 970 doesn't perform like the GTX 980).

So, is the rumor true? Why did Nvidia hamstring the GTX 970? How did they manage to slow the access to certain addresses in the memory VRAM but not others? If a game does end up using the slowed memory does it make a significant difference in FPS or frame-time latency?

Pretty old news with plenty of old forums posts about this. Yes, your game will suffer if it needs more than 3.5gb of space, but is still pretty rare to encounter in the real world.

Supertrucker · Sep 25, 2015

So a 970 is a cut down 980. Parts of the chip are disabled either due to defects or simple demand for the 970. Lower shader count and all that. In the cutting down, you lose some of the interface between the gpu and the memory.

To get around that nvidia segmented the memory into a 3.5gb pool with high speed/high priority access and a .5gb pool with low speed/low priority access. The drivers try to not use more than 3.5 gb if they can help it. Because if you end up needing that last .5gb (notice I said needing and not simply using) then it will feel a lot like when you run out of vram and the system has to swap from your system ram.

It's quite hard to work yourself into a situation where you need more than 3.5gb of vram but not more than 4gb, but it can happen. And there is no fixing it. It's built into the hardware.

http://wccftech.com/nvidia-geforce-gtx-970-memory-issue-fully-explained/ if you want to read more.

Kenrou · Sep 26, 2015

Supertrucker said:
It's quite hard to work yourself into a situation where you need more than 3.5gb of vram but not more than 4gb, but it can happen. And there is no fixing it. It's built into the hardware.

http://wccftech.com/nvidia-geforce-gtx-970-memory-issue-fully-explained/ if you want to read more.

Start using MSAA 8x or more in today's games and you see the memory disappearing very fast...

EarthDog · Sep 26, 2015

There are exceptions, no doubt. For most, at 1080p, this is a non issue though.

NiHaoMike · Sep 26, 2015

Something else that can help is for the driver to put 2D stuff like browsers in the 512MB first. When I forced Firefox into using the 512MB, Facebook appeared to scroll as fast as it normally does, even on a 4K display.

magellan · Nov 11, 2015

Has this GTX 970 slowed memory access bug been fixed w/newer versions? I'm thinking of buying a pair, but if they're still gimped I won't bother.

jaymz9350 · Nov 11, 2015

It's not a "bug" it's the design and I don't think they changed it. Now I have a pair and have seen a few hiccups but in these games I can top out over 4 GB so it really wouldn't matter if they changed it.

That said I'd grab a 980ti over a pair of 970's now personally, those weren't out yet when I got my 970's

EarthDog · Nov 11, 2015

the ram isnt really slower, it just works slower as its on a narrower bus width. but 3.5gb will run at 7/8 speed and .5gb will run at 1/8 speed if it the card is using more than the first 3.5gb

The first 3.5GB run full speed, not 7/8. Its the .5GB that is gimped only.

magellan said:
Has this GTX 970 slowed memory access bug been fixed w/newer versions? I'm thinking of buying a pair, but if they're still gimped I won't bother.

http://wccftech.com/nvidia-geforce-gtx-970-memory-issue-fully-explained/

Grab a 980 if you dont want to worry about the memory issue. 980ti is in a class by itself.

There as a large thread here on the subject as well... feel free to look around the forums and the internet. It has been covered ad nauseum.

magellan · Nov 11, 2015

jaymz9350 said:
It's not a "bug" it's the design and I don't think they changed it. Now I have a pair and have seen a few hiccups but in these games I can top out over 4 GB so it really wouldn't matter if they changed it.

That said I'd grab a 980ti over a pair of 970's now personally, those weren't out yet when I got my 970's

Games using more than 4 GiB -- that's crazy. What games top out at over 4 GiB? I read GTA V gets near 4 GiB, but I haven't read about any games going over 4 GiB yet.

caddi daddi · Nov 11, 2015

I play gtav at 1440 with a 970, I have to turn a few things down but nothing I could say is memory related
I just don't have to power of a 980.
at 1080 I can crank all the graphics up and have no issues at all.

jaymz9350 · Nov 11, 2015

magellan said:
Games using more than 4 GiB -- that's crazy. What games top out at over 4 GiB? I read GTA V gets near 4 GiB, but I haven't read about any games going over 4 GiB yet.

Dying Light I noticed toping 5 when I replayed it with no issues, the first couple times it was 3.8ish with hiccups occasionally topping 4. I beleive Shadow of Moridor also peaked over 4 and GT6 V does top 3.5 with no issues

ATMINSIDE · Nov 11, 2015

jaymz9350 said:
Dying Light I noticed toping 5 when I replayed it with no issues, the first couple times it was 3.8ish with hiccups occasionally topping 4. I beleive Shadow of Moridor also peaked over 4 and GT6 V does top 3.5 with no issues

How, exactly, did you hit 5GB of vRAM used on a 4GB GPU??

jaymz9350 · Nov 11, 2015

If I recall vram pages to system ram if full, not the first case I've had of this. Skyrim peaked around 1.5 at times on my 1 GB 5870. These numbers are what afterburner gives me.

GTX 970: what was the slower memory issue all about?

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