# 256 vs 384 vs 512



## Nosada (Sep 19, 2014)

With the benchmarks released for the new batch of nVidia cards, I've been debating the use of bigger memory buswidth, but I don't feel I have all the facts to form an unbiased opinion on this matter.

Actual bandwidth of the memory-bus is dependant on speed of the memory and width of the bus, that much seems obvious. Lately it seems however, that with 7Ghz memory on most videocards, the buswidth is becoming less and less the deciding factor. An R9 285 doesnt perform worse than a R9 280 despite having a bus a third narrower. Same goes for the new GTX970 compared to an R9 290X or GTX780.

So am missing something obvious? Does buswidth have an advantage at QHD resolutions only, or is it basically a moot point at this time due to no more bandwidth being required for the current generation of games?


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## rtwjunkie (Sep 19, 2014)

As I understand it, the faster the memory, the less of a need for 384 and 512 bandwitch...to a point.  Of course I'm sure there are didminishing returns, but as it stands now, 256 seems to be enough at 7Ghz(+) memory speeds.  Of course, I'd still be all over a 384 bit if it was released....as I anticipate a GM200/GM210 chip will be.


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## Frick (Sep 19, 2014)

If a wider buswidth would automatically mean more data being shoveled thru it it would matter, but as you say it doesn't.


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## rtwjunkie (Sep 19, 2014)

Frick said:


> If a wider buswidth would automatically mean more data being shoveled thru it it would matter, but as you say it doesn't.


 
Well said!


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## EarthDog (Sep 19, 2014)

> Does buswidth have an advantage at QHD resolutions only


For the most part... there you have it! When you pour on the eye candy, specifically AA, you would want more bandwidth and memory.

(you may want to consider putting a more descriptive title on this thread...)


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## Vario (Sep 19, 2014)

Usually its better to buy larger bandwidth cards.  Kepler doesn't seem as sensitive to bus size as prior generations.


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## Vayra86 (Sep 19, 2014)

The bandwidth dependancy MUST be brought back on GPU's for the near future, as 1440p / 2160p are becoming the norm. This is being pushed right now but the limits of the current architecture are definitely in sight.

Both Nvidia and AMD are making moves now to reduce bandwidth dependancy. As far as we know at this time, Tonga manages to stay on par with a 384bit wide 280x on a 256bit bus. On the Nvidia side of things, we've seen slides where they market Maxwells reduction of bandwidth dependancy, which should decrease by about 25%. That is considerable. The biggest profits are likely offloading data to a bigger cache, and this is a move that Nvidia has already started to implement with driver updates that include Shader Cache. Maxwell builds on that idea by also providing a larger cache and using it differently. Texture streaming is rapidly becoming more efficient and as soon as streaming introduces similar latency to 'storing in memory', bus width is kind of obsolete.

Quite sure this isn't the whole story, but the bottom line is that it's clear that the days of 'bus width above all else' are finally over.


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## EarthDog (Sep 19, 2014)

Ahh, the miracles of compression...

When was it ever bus width over everything else? I have to admit I never bought a GPU on that premise until 4K gaming came about. 256bit is still fine on 5760x1080...


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## Vario (Sep 19, 2014)

EarthDog said:


> Ahh, the miracles of compression...
> 
> When was it ever bus width over everything else? I have to admit I never bought a GPU on that premise until 4K gaming came about. 256bit is still fine on 5760x1080...


2006?


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## EarthDog (Sep 19, 2014)

Hah, something like that. Not recently, that is for sure.


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## Vayra86 (Sep 19, 2014)

Sure it was. GTX 660ti was limited by its 192 bit bus, one of the major gripes of this card.

Many lower end/midrange cards are definitely limited by bus width / bandwidth, being able to do more with a similar bus is a good way to cut costs. Same reason we saw 256 bit with 7 Ghz mem on 7xx.


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## EarthDog (Sep 19, 2014)

Its a low end/midrange card. Its not meant to play well at over 1080p. 

+1 to cutting costs. But I still don't know who shopped by 'buswidth over anything else' except the misinformed. In the vast majority of cases it is much ado about nothing.


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## rtwjunkie (Sep 19, 2014)

Vayra86 said:


> Sure it was. GTX 660ti was limited by its 192 bit bus, one of the major gripes of this card.
> 
> Many lower end/midrange cards are definitely limited by bus width / bandwidth, being able to do more with a similar bus is a good way to cut costs.


 
Very true.  Basically the 660Ti could have very nearly been a 670 (and depending on model, could surpass the 670 on certain games.  Just imagine what kind of a card it could have been without it's bandwidth artificially capped at 192 bit?!


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## RCoon (Sep 19, 2014)

EarthDog said:


> Its a low end/midrange card. Its not meant to play well at over 1080p.
> 
> +1 to cutting costs. But I still don't know who shopped by 'buswidth over anything else' except the misinformed. In the vast majority of cases it is much ado about nothing.



In the event manufacturers find bandwidth lacking, they probably won't waste money on a bigger bus. My best bet is they'll just find a better compression technique until they're stuck at an impass (LOL chrome tried to auto-correct that to imp ass) of computational limitation and then increase the bus width.
Not to mention those wider buses seem to get a little warmer...


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## EarthDog (Sep 19, 2014)

RCoon said:


> In the event manufacturers find bandwidth lacking, they probably won't waste money on a bigger bus. My best bet is they'll just find a better compression technique until they're stuck at an impass (LOL chrome tried to auto-correct that to imp ass) of computational limitation and then increase the bus width.
> Not to mention those wider buses seem to get a little warmer...


Its cheaper to put faster ram on a lesser bus too.



rtwjunkie said:


> Very true.  Basically the 660Ti could have very nearly been a 670 (and depending on model, could surpass the 670 on certain games.  Just imagine what kind of a card it could have been without it's bandwidth artificially capped at 192 bit?!


A 670... let's jump for joy that it could be a card that already exists.


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## rtwjunkie (Sep 19, 2014)

EarthDog said:


> A 670... let's jump for joy that it could be a card that already exists.


 
LOL!  No, what I was saying was Nvidia artificially crippled 670's basically to make 660Ti's.  And depending on the maker, and how they tuned them or replaced components, it still held it's own against the 670.  So, I wasn't saying it was almost a card that already existed, it was created and intentionally crippled, with the primary factor being to cut the bandwidth.  That kept them from losing 670 sales with a card issued to meet a lower price point.

It was quite a good card in it's day only a couple years ago.  660's were midrange...the Ti was aimed at lower high end.


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## EarthDog (Sep 19, 2014)

I understood what you said/meant... I was having some fun with it was all.


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## Aquinus (Sep 19, 2014)

The size of the memory data bus should match the capabilities of the GPU. There is no point to pair a really wide memory bus with a GPU that can't take advantage of it. Also keep in mind that when you have a data bus that wide, you need to pull that many bits out of memory as well and to use memory optimally you need to be able to get data into the GPU's shader cache as quickly as you read it out of memory. So making the data bus wide isn't just doubling the number of transistors to do it, keep that in mind too because there are costs to widening *any* bus in an integrated circuit with respect to latency and circuit complexity.


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## Vayra86 (Sep 19, 2014)

EarthDog said:


> Its a low end/midrange card. Its not meant to play well at over 1080p.
> 
> +1 to cutting costs. But I still don't know who shopped by 'buswidth over anything else' except the misinformed. In the vast majority of cases it is much ado about nothing.



Oh yeah they did. That is what AMD enthusiasts said to Nvidia enthusiasts when comparing HD7000 to Kepler. And they are right too, HD's play better with high resolutions and lots of AA, from the 7870 onwards, compared to 600 series Nvidia. There is more in the market than absolute high end cards you know  For Kepler the limited buswidth was an issue on the GK106 and GK104 until they refreshed it and memory overclocks were almost 1:1 performance increases.


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## EarthDog (Sep 19, 2014)

I know.. but it still doesn't matter!!! People were all too hung up on that for no reason. Its simple people. Look at the performance of the card at your resolution. Is it good enough? Get it. Don't sweat these cheesy details (unless you are rocking 4K - which is new to the landscape which goes right back to my point... who does that is misinformed on what is important and for most its a non issue).


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## Vayra86 (Sep 19, 2014)

Back in 2012 for people who were pushing 1440p, that 256bit bus on 670 was holding them back from doing so without stutter and 7970 performed a lot better on similar price points.

Something similar is happening today with current gen GPU's and 4k.

Sorry but I really can't agree it's a non-issue. Bandwidth is a hot topic every gen and for 900 series it shows that the actual energy savings are made by advances in the way they treat and use the bus width  We also know from the microstutter chit-chat that simple FPS tables don't say jack shit about actual gaming smoothness, and memory plays a major role in this.


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## rtwjunkie (Sep 19, 2014)

EarthDog said:


> I understood what you said/meant... I was having some fun with it was all.


 
Yeah, I knew, to a degree, hence the "LOL" (and I chuckled at my computer).  I actually  I did think it was funny, but felt the need to explain better for everyone's benefit, too.


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## EarthDog (Sep 19, 2014)

Vayra86 said:


> Back in 2012 for people who were pushing 1440p, that 256bit bus on 670 was holding them back from doing so without stutter and 7970 performed a lot better on similar price points.
> 
> Something similar is happening today with current gen GPU's and 4k.
> 
> Sorry but I really can't agree it's a non-issue. Bandwidth is a hot topic every gen and for 900 series it shows that the actual energy savings are made by advances in the way they treat and use the bus width  We also know from the microstutter chit-chat that simple FPS tables don't say jack shit about actual gaming smoothness, and memory plays a major role in this.


I'll also disagree with some points...

1. It wasn't the bus so much as it was the 2GB vram on those cards. The 4GB 670's did just fine there (for my uses) (and so does the 770 4gb). I do not recall an article that actually pinned down the problem to the bus...but then again, the interwebs are huge and I may have missed it... and my 'butt dyno' could be off too, LOL!
2. Energy savings... cool. Sorry, I am caffeine free this morning. Can you associate that point with what we are talking about? Sorry..
3. Correct FPS tables do not show the whole story. Then again, I do not recall any frametime reviews/studies/articles on bandwidth. Link me so I may learn.


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## rtwjunkie (Sep 19, 2014)

Overall, I'm going to have to agree with EarthDog, in that with the new GPU's, and most instances of 7 series Kepler, bandwidth is not so much an issue now.  If the memory is fast enough, coupled with the compression, 256-bit is enough.  The primary thing holding cards back from higher resolutions was the amount of VRAM.  Now with Maxwell, we've got a minimum of 4GB VRAM at 7000Ghz.  I think the future is here!

That being said, I'd still opt a wider bus if a model came out with it.


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## Vayra86 (Sep 19, 2014)

1. Bus width has a direct impact on the amount of texture streaming that is possible. Less VRAM on the card will mean more texture streaming (and swapping) is necessary to maintain a smooth gaming experience. So the 4GB cards handled that resolution better. A 2GB card with a larger bus would have handled it just as well (or would at least show better smoothness). But slapping an additional 2GB VRAM on it is cheaper than adjusting bus width. The 7970 proves this point by combining 3 GB with a 384 wide bus and offering the best performance at the time for high res/high AA.

2. Not directly associated, just pointing out that bus width is an important factor in GPU design and also in required power. You could connect this to overclockability though. Smaller bus = less power = more OC headroom for GPU/mem.

3. Frame delivery depends on the entire rendering pipeline. This ties in to 1. You can have 60 fps average with stutters and a shit gaming experience.

I do agree that for the average gamer/buyer this is a worthless discussion and in 95% of the cases GPU/bus width are balanced. But this is a tech site. We whine about that last 2% of performance. So that's what I do


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## Vario (Sep 19, 2014)

EarthDog said:


> Hah, something like that. Not recently, that is for sure.


I'll just say I've regretted buying cards with small bus widths in the past, but that was like 2006.  BFG 7600 GT OC I traded up to a EVGA 7800GT, and that extra bus width helped a ton, 128 to 256.  Frame rate for BF2 at the time was much smoother.

However 384 bit 7970 to 256 bit 770 on my 1080P, 770 is just a tiny bit faster but otherwise not noticeable.


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## newtekie1 (Sep 19, 2014)

Something that I don't think has been brought up, but may have been, is that GDDR5 is actually Quad-Data Rate.  So right there, you've basically doubled the memory bandwidth.  So a 256-Bit GDDR5 bus has the same bandwidth as a 512-Bit GDDR3/4 bus.

That has helped remove the memory bus bottleneck significantly.  We basically are to the point where a 256-bit GDDR5 bus is enough, and going higher doesn't really yield any significant gains.  This is true all the way up to 4k resolution.  Just look at the 780Ti vs 980Ti benchmarks.  Despite the 780Ti having a wider memory bus, the 980Ti is ~7% faster at both 1080p and 4K.


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## EarthDog (Sep 19, 2014)

There were more differences than that between the 7600GT and 7800GT (pixel pipelines... clock speeds..etc).

You really cannot compare, at least empirically, between the brands/cards and with confidence say it was the bandwidth that is the main difference. It would have to be the same card with the ONLY difference being the bandwidth (which is difficult unless you compared 256 to 512 and 384 to 768 as you cannot have the same memory capacities with the differing bus amounts - example you can't have 3GB on 256 bit bus without having a mixed architecture). Also 2GB on 1080p is really the minium these days. For example, look at BF4. At 1080p default Ultra settings, it will go over 2GB of use.



Vayra86 said:


> 1. Bus width has a direct impact on the amount of texture streaming that is possible. Less VRAM on the card will mean more texture streaming (and swapping) is necessary to maintain a smooth gaming experience. So the 4GB cards handled that resolution better. A 2GB card with a larger bus would have handled it just as well (or would at least show better smoothness). But slapping an additional 2GB VRAM on it is cheaper than adjusting bus width. The 7970 proves this point by combining 3 GB with a 384 wide bus and offering the best performance at the time for high res/high AA.
> 
> 2. Not directly associated, just pointing out that bus width is an important factor in GPU design and also in required power. You could connect this to overclockability though. Smaller bus = less power = more OC headroom for GPU/mem.
> 
> ...


1. So you agree with me... nice.

2. Gotcha.
3. Right. I agree with that point. 

What I took exception to was your earlier statement of 'bus width over everything else'. That was never the thinking AFAIK.


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## Vayra86 (Sep 19, 2014)

newtekie1 said:


> Something that I don't think has been brought up, but may have been, is that GDDR5 is actually Quad-Data Rate.  So right there, you've basically doubled the memory bandwidth.  So a 256-Bit GDDR5 bus has the same bandwidth as a 512-Bit GDDR3/4 bus.
> 
> That has helped remove the memory bus bottleneck significantly.  We basically are to the point where a 256-bit GDDR5 bus is enough, and going higher doesn't really yield any significant gains.  This is true all the way up to 4k resolution.  Just look at the 780Ti vs 980Ti benchmarks.  Despite the 780Ti having a wider memory bus, the 980Ti is ~7% faster at both 1080p and 4K.



980 also has more processing power doesn't it? Not sure its attributable to bus in either case I think they are both maxed on core. The only reason 256bit bus is still enough on Maxwell is because they now use higher rated memory, larger cache and better compression. These are all things that allow them to keep bus width at 256bit, keeping it paced with the capabilities of the GPU. If what you were saying was true, AMD would have never adopted 512 bit. They do this because they also use lower rated memory.

Limiting bus width is a cost and arch consideration at all times, and the best way to cut cost. Nvidia has a better grasp on this than AMD.


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## Mathragh (Sep 19, 2014)

The biggest reason modern high end graphics cards can still make do with a fairly small bus is because:


1: the datarate per bitlane has gone up tremendously, with GDDR5 being able to transfer 4 bits per clock, and clocking very high.

2: GPUs are increasingly intelligent when it comes caching, with the newest Nvidia GPU amongst other things having 2MB of L2 cache which has a very high bandwidth and causes the GPU to not have to acces the main memory as often -> reducing bandwidth needed from the main memory.

3: Modern GPUs all use some sort of compression techniques, where instead of simply copying all the data bit-for-bit to the memory every time, it on the fly compresses this data in multiple ways causing the bandwidth needed to decrease in a very significant way.

4: All kinds of architectural changes in modern GPU architectures that don't fall under the previous 3.

While it might seem easy to just say: " The use of high frequency GDDR5 causes this card to not need that big of a bus!", it actually is all these things combined that cause the card to only "need" its current bus size. There also doesn't really seem to be a hard rule as to what bus size/speed is the best, but instead it always is the result of the trade-off architects make when optimising GPU efficiency compared to die space and poweruse.

Edit: Specifically regarding your question:
It would seem memory frequency in combination with a more efficient use of memory bandwidth as a result of all the other improvements mentioned above result in a 256bit bus still being sufficient for the current gen, as the 256bit nvidia 980 is clearly outperforming cards with a bigger bus. Furthermore, as the 780 Ti has a 384bit bus with the same frequency memory, apparently nvidia found a way to make the bandwidth use itself more efficient. A couple of things they mentioned themselves regarding bandwidth was the 2MB L2 cache and better compression techniques.


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## yogurt_21 (Sep 23, 2014)

it tends to matter across the same gpu generation as it's tied in with the number of ROP's, so a 192-bit with a higher mem speed might produce the same memory bandwidth, but I'm pretty sure you're going to notice a 25% reduction in ROP's. 

across different gens/manufacturers doesn't matter as much. 
my R9 290 has 512-bit mem at 5GHZ effective clock for 320GB/s 
the 980 has 256-bit memory at 7GHZ effective for 224GB/s 
yet the 980 offers 144Gtexel/s in texture fill rate just a few percentage pts behind the 290's 152 Gtexel/s fill rate  it does this despite having far less memory bandwidth and 32 fewer texture memory units. This is why it's important to only compare memory bandwidth within the same gpu manufacturer and generation. Otherwise it's just going to mislead you. On paper the R9 290X has more memory bandwidth, more texture fillrate, more floating point performance, and 1 million more transistors. It doesn't change the fact that it gets spanked by the 980 in actual gaming performance.


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## eidairaman1 (Sep 23, 2014)

The narrower the bus is the higher the frequency the parts have to be.


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## EarthDog (Sep 24, 2014)

You are just full of arbitrary one liners, aren't ya?


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## eidairaman1 (Sep 24, 2014)

EarthDog said:


> You are just full of arbitrary one liners, aren't ya?



Lol I can be just that i noticed if the bus is wider the less frequency you need.


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