Help understanding GPU specs

[Shaqo_Wyn]

Hi!

 

So I've never really paid much attention to GPU's in terms of the specs they have. I usually just check out a few reviews and benchmarks, gauge the general opinion and decide based on that. 

 

I know the basic stuff that's important: amount of VRAM, bus-width, base clock and memory clock right?

 

If anything I care more about how they perform in terms of noise and thermals. 

 

This brings me to my question/confusion. How does a GPU's specs determine it's performance?

 

Like the GTX 780 has 3GB of VRAM and a 384-bit bus. I've seen people say many times on this forum that the 6GB version isn't worth it because the 384-bit bus can't efficiently utilize 6GBs. 

 

At the same time, the GTX 880 rumor mill seems to be pointing towards 4GBs on a 256-bit bus and I've read people say it's going to be better than the 780. In my head this doesn't make sense, more VRAM and a smaller bus when a 384-bit can't handle 6GBs?  This while AMD has 4GB's on 512-bit bus. But you probably can't compare AMD to Nvidia in this respect.

 

Go easy on me bruhs, I really don't know much about this stuff as up until now I've never bothered to dive deep into it. So apologies if I f-ed up on the stats and jargon. Any explanation/info or links where I can read up on the subject is much appreciated. 

 

Cheers!

 

Shaqo

[Lord Pantaloons]

I have 4GB 760's and they have a 256 bit bus, while playing watchdogs I hit my 4GB cap several times. A 256 bit bus can use 4GB.

[lachyman]

You miss one very important factor - amount of CUDA cores/stream processors. That is the biggest factor that determines GPU performance. More is better, but you can't compare apples and oranges, a Maxwell core is stronger than a Kepler core, so when you have for example 1000 Maxwell cores and 1200 Kepler cores, the Maxwell is still better. Second comes clockspeed which you probably understand. I call these 2 factors active, because more is always better. VRAM and bus width are static factors, because you only need a set amount before more starts to be useless. 3GB is the most you will ever need for 1080p, that's why a 3GB 780 is better than a 4GB 760, even though it has less memory.

[Shaqo_Wyn]

You miss one very important factor - amount of CUDA cores/stream processors. That is the biggest factor that determines GPU performance. More is better, but you can't compare apples and oranges, a Maxwell core is stronger than a Kepler core, so when you have for example 1000 Maxwell cores and 1200 Kepler cores, the Maxwell is still better. Second comes clockspeed which you probably understand. I call these 2 factors active, because more is always better. VRAM and bus width are static factors, because you only need a set amount before more starts to be useless. 3GB is the most you will ever need for 1080p, that's why a 3GB 780 is better than a 4GB 760, even though it has less memory.

Thanks! Interesting. So CUDA cores and clock speed are really important. Is there a fixed table or reference point for the static factors. Say max 4GB for 256-bit or in correlation to the screen resolution? Like why do people say for example that the GTX 780 can't efficiently utilize 6GB because of it's 384-bus? 

[Shaqo_Wyn]

I have 4GB 760's and they have a 256 bit bus, while playing watchdogs I hit my 4GB cap several times. A 256 bit bus can use 4GB.

Yeah I figured, I think the 770 comes in a 4GB version too but I've also seen people say that the 4GB version of the 770 isn't worth it either. 

[lachyman]

Thanks! Interesting. So CUDA cores and clock speed are really important. Is there a fixed table or reference point for the static factors. Say max 4GB for 256-bit or in correlation to the screen resolution? Like why do people say for example that the GTX 780 can't efficiently utilize 6GB because of it's 384-bus? 

A rule is that there should be 128bit width for every 1GB of VRAM, so 256bit for 2GB, 384bit for 3GB and so on. That's the perfect ratio, but less can work very well too, I used to have a 660 that was 2GB/192bit and it maxed out the 2GB no problem. 128bit would probably have issues though and only utilized around 1.5GB.

[Shaqo_Wyn]

A rule is that there should be 128bit width for every 1GB of VRAM, so 256bit for 2GB, 384bit for 3GB and so on. That's the perfect ratio, but less can work very well too, I used to have a 660 that was 2GB/192bit and it maxed out the 2GB no problem. 128bit would probably have issues though and only utilized around 1.5GB.

Oke. Two more questions, just to make sure I understand this. So this means that 4GB on 256-bit bus like with the the GTX 770 isn't that good right? However it won't be a problem on the GTX 880 as that is Maxwell based which is more powerful? 

[lachyman]

Oke. Two more questions, just to make sure I understand this. So this means that 4GB on 256-bit bus like with the the GTX 770 isn't that good right? However it won't be a problem on the GTX 880 as that is Maxwell based which is more powerful? 

VRAM clockspeed can be a workaround just as a lot of other high-level stuff I myself don't understand, but NVIDIA uses them so I myself guess (and hope) the 880 can use all it's VRAM despite the narrow bus. I think GK110 had some unique abilities so it could use all 6GB, that may be the case here as well. But 8GB on 256bit is just pure bullshit. And yeah a 770 can't use 4GB also it's just GK104.

[i_build_nanosuits]

Cuda cores for nvidia and stream processors for AMD is the MAIN spec to look for when compairing cards, the performances in games will be determined by how many cores the GPU run's and how fast (tha gigahurtz man)

Taking into consideration the overclocking potentital of each GPU is also important.

VRAM amount, VRAM speed, and bus width will have ''IN MOST SCENARIOS'' next to no effect on performance ''UNLESS YOU STRESS THE MEMORY A LOT AND/OR RUN OUT OF VRAM''

[D2ultima]

Ok ok hold on here. vRAM and memory bus width are not particularly linked. I don't know about the poster above who had a 128-bit card that couldn't max 1.5GB of vRAM, but 256-bit maxes 4GB VERY easily without performance hits, and the GTX 880M is 256-bit with 8GB vRAM, which they wouldn't put if it was inaccessible past 4GB.

 

Here's what. vRAM is simply how much available graphics memory you have. Rendering your desktop, rendering your game, rendering effects, whatever? All of this uses video RAM. The amount of vRAM used depends solely on what is being rendered. It does NOT mean that more vRAM being used is better, it simply means that the data is higher. For example: Titanfall uses 3-3.6GB of vRAM on my machine if I use insane textures, but BF 4 uses only 2-2.3GB and looks better. And Prototype 2 has better-looking textures than Titanfall does, but won't pass 1GB of vRAM usage.

 

In short, the more vRAM you have, usually the better. The original GTX Titan had a problem using all 6GB of its memory buffer, but the Titan Black should have no such issues. 780 and 780Ti 6GB versions are fine and I actually recommend them to people. I think 4GB of vRAM should be a standard for gaming these days; especially with how unoptimized games are becoming due to the current-gen consoles having so much available memory. It's a reason I shouldn't have to cite, but it is the reason.

 

Anyway, 4GB 770s and 4GB 760s are all I recommend if someone has the money. I never recommend 2GB cards anymore. Most people don't understand that vRAM is per-game usage, and more vRAM being used DOES NOT MEAN that the game's graphics are more demanding. It just means it's using more vRAM. Skyrim uses ~40% of my GPUs and will happily grab 2.7GB of vRAM while Dark Souls 2 at 4k res will max both my GPUs out and struggle to maintain 60fps constant (with all the graphics maxed anyway) but only use 1.4GB of vRAM.

 

Anyway, memory speed and memory bus width go hand in hand. A 6000MHz memory clock on a 256-bit memory bus using GDDR5 is the same as a 128-bit memory bus, 12000MHz memory clock card using GDDR5. It's also the same as a 512-bit memory bus with a 3000MHz memory clock on GDDR5. It just means how fast the memory is, and honestly, it doesn't have a huge impact on most games. You want more, of course, but it doesn't mean it's super necessary.

 

As for clock speeds on the card, core count and clock speeds work in tandem. Considering kepler versus kepler (all gaming-class 600 and 700 series cards except the 750Ti which is maxwell) you simply do a multiplication and compare. If one card is 1000MHz core clock with 1000 cores, it's 2/3 the strength of another card with 1000MHz core clock and 1500 cores. You can use that to see a comparison of how strong or weak they are relative to each other. I don't know exactly how AMD's is calculated, but you can get a good guideline from that.

[i_build_nanosuits]

Ok ok hold on here. vRAM and memory bus width are not particularly linked. I don't know about the poster above who had a 128-bit card that couldn't max 1.5GB of vRAM, but 256-bit maxes 4GB VERY easily without performance hits, and the GTX 880M is 256-bit with 8GB vRAM, which they wouldn't put if it was inaccessible past 4GB.

True, 16GB of VRAM could be filled on a 64bits memory bus...it would simply take longer and be unpracticle for gaming but it could defenetly happen with the right software, VRAM has no effect on gaming it's simply used to store textures and some other stuff...most games at 1080P run's fine maxed out with only 2gb but some of them are now starting to require more VRAM even at 1080p thus making 2gb cards recommendations a little harder these days unless it's for a cheap mid-range GPU (R9 270...GTX 760...etc.)

[Techhog]

Because the people saying that the bus can't handle it are being dumb. It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI.

[D2ultima]

Because the people saying that the bus can't handle it are being dumb. It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI.

But this is the point I made: You don't *HAVE* to run out of GPU power before running out of vRAM. I proved that in my post above, where I could use up 2.7GB+ on Skyrim with 40% GPU usage while Dark Souls 2 maxed at 4k res used only 1.4GB (if so much) but maxed both my 780Ms running at GTX 680 clock speeds.

[i_build_nanosuits]

Because the people saying that the bus can't handle it are being dumb. It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI.

again, this is only partly true...the fact that a game require more or less VRAM is purely and only due to the quality (resolution) of the in-game textures...and running higher quality textures won't require additionnal processing power...it only require more space (VRAM) to store those high-quality textures, here:

 

http://lifehacker.com/5985304/get-the-most-from-your-games-a-beginners-guide-to-graphics-settings

[Techhog]

But this is the point I made: You don't *HAVE* to run out of GPU power before running out of vRAM. I proved that in my post above, where I could use up 2.7GB+ on Skyrim with 40% GPU usage while Dark Souls 2 maxed at 4k res used only 1.4GB (if so much) but maxed both my 780Ms running at GTX 680 clock speeds.

 

 

again, this is only partly true...the fact that a game require more or less VRAM is purely and only due to the quality (resolution) of the in-game textures...and running higher quality textures won't require additionnal processing power...it only require more space (VRAM) to store those high-quality textures, here:

 

 

ttp://lifehacker.com/5985304/get-the-most-from-your-games-a-beginners-guide-to-graphics-settings

 

These come into play generally only in extreme examples, especially in the case of modded Skyrim. I'm talking about in general.Unless you're trying to argue that it's likely that most upcoming games will use more than 3GB at 1080p, you're not saying anything contrary to what i said. There are exceptions to everything.

[D2ultima]

Because the people saying that the bus can't handle it are being dumb. It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI.

 

 

These come into play generally only in extreme examples, especially in the case of modded Skyrim. I'm talking about in general.Unless you're trying to argue that it's likely that most upcoming games will use more than 3GB at 1080p, you're not saying anything contrary to what i said. There are exceptions to everything.

 

You don't have to run out of GPU power before you run out of vRAM. The two are not linked. Titanfall happily eats up nearly 4GB of vRAM, but is far less demanding than Crysis 3, which will eat up say 2.4GB? It's game-dependent and cannot be used as a reference.

 

I am not saying that 6GB 780s are a bad idea; in fact it's a great idea. A lot of developers are getting sloppy and displaying their sub-par-ness; they got more than 512MB of memory on consoles so now half the games use 3-4GB of vRAM on PC. I don't recommend 2GB cards at all anymore; even if someone's buying a 760. But a 760 can easily use 4GB of vRAM without hitting 100% usage 1080/60 in some games, whereas in others it'll barely manage 1080/30 on medium settings while happily using 1.2GB of vRAM. It just depends on the game.

 

And again, the resolution matters about as much as whether you eat eggs for breakfast 1 day in the week or no days in the week. I could use 2.5GB of vRAM in Arma 2 with an internal render resolution of 720p while Dark Souls 2 at 4k res won't touch 1.5GB. If the game is going to use a lot of vRAM, the resolution matters little. That's all there is to it.

 

Man I really need to make a vRAM info thread.

[Techhog]

You don't have to run out of GPU power before you run out of vRAM. The two are not linked. Titanfall happily eats up nearly 4GB of vRAM, but is far less demanding than Crysis 3, which will eat up say 2.4GB? It's game-dependent and cannot be used as a reference.

 

I am not saying that 6GB 780s are a bad idea; in fact it's a great idea. A lot of developers are getting sloppy and displaying their sub-par-ness; they got more than 512MB of memory on consoles so now half the games use 3-4GB of vRAM on PC. I don't recommend 2GB cards at all anymore; even if someone's buying a 760. But a 760 can easily use 4GB of vRAM without hitting 100% usage 1080/60 in some games, whereas in others it'll barely manage 1080/30 on medium settings while happily using 1.2GB of vRAM. It just depends on the game.

 

And again, the resolution matters about as much as whether you eat eggs for breakfast 1 day in the week or no days in the week. I could use 2.5GB of vRAM in Arma 2 with an internal render resolution of 720p while Dark Souls 2 at 4k res won't touch 1.5GB. If the game is going to use a lot of vRAM, the resolution matters little. That's all there is to it.

 

Man I really need to make a vRAM info thread.

*sigh* I mean in most cases. Here, let me reword it in a way you people will understand.

 

For most games at 1080p or 1440p on max settings, the GPU will be the bottleneck before the VRAM is, most games don't use that much VRAM at those resolutions. However, there are are exceptions. This should go without saying, however, because there are always exceptions to everything.

 

Tell me if I need to get more specific. I can't believe that I actually need to state that I don't mean for every single game. I really hope you were just assuming that I don't know anything and you were just trying to educate me. I'll be more specific from now on. I sometimes forget how used to having to dumb things down some of us are. I won't be needing that VRAM thread, tyvm.

[Shaqo_Wyn]

You don't have to run out of GPU power before you run out of vRAM. The two are not linked. Titanfall happily eats up nearly 4GB of vRAM, but is far less demanding than Crysis 3, which will eat up say 2.4GB? It's game-dependent and cannot be used as a reference.

I am not saying that 6GB 780s are a bad idea; in fact it's a great idea. A lot of developers are getting sloppy and displaying their sub-par-ness; they got more than 512MB of memory on consoles so now half the games use 3-4GB of vRAM on PC. I don't recommend 2GB cards at all anymore; even if someone's buying a 760. But a 760 can easily use 4GB of vRAM without hitting 100% usage 1080/60 in some games, whereas in others it'll barely manage 1080/30 on medium settings while happily using 1.2GB of vRAM. It just depends on the game.

And again, the resolution matters about as much as whether you eat eggs for breakfast 1 day in the week or no days in the week. I could use 2.5GB of vRAM in Arma 2 with an internal render resolution of 720p while Dark Souls 2 at 4k res won't touch 1.5GB. If the game is going to use a lot of vRAM, the resolution matters little. That's all there is to it.

Man I really need to make a vRAM info thread.

Good point. Makes perfect sense to me. Maybe you should make that thread. It'll probably ignite more discussion though.

I have one question about the resolution though, why do people say that more vRAM is good at higher resolutions like 4K?

[Techhog]

Good point. Makes perfect sense to me. Maybe you should make that thread. The GPU section definitely needs it.

I have one question about the resolution though, why do people say that more vRAM is good at higher resolutions like 4K?

Because it does have an effect, and his main example of it not having an effect is a last-gen console port with a framerate cap.

[D2ultima]

Good point. Makes perfect sense to me. Maybe you should make that thread. It'll probably ignite more discussion though.

I have one question about the resolution though, why do people say that more vRAM is good at higher resolutions like 4K?

It's generally thought of that high resolutions = more vRAM usage. It's not particularly wrong, so to speak, but it's not like 1080p = 2GB used and 4k = 4GB used. In-game settings have FAR more to do with it. Also, playing in windowed mode or borderless fullscreen uses more vRAM. When you fullscreen you usually snap off the desktop's render, which frees up more vRAM, but multiple monitors still render when you're in fullscreen. So usually for multiple monitors people make sure you have extra vRAM, but 2GB has been pretty much ok for most people up until maybe last year. NOW I think the more the better, both due to lazy devs and higher resolution monitors becoming mainstream. I'd love to find me some 8GB 880MX maxwell GPUs next year .

[Techhog]

It's generally thought of that high resolutions = more vRAM usage. It's not particularly wrong, so to speak, but it's not like 1080p = 2GB used and 4k = 4GB used. In-game settings have FAR more to do with it. Also, playing in windowed mode or borderless fullscreen uses more vRAM. When you fullscreen you usually snap off the desktop's render, which frees up more vRAM, but multiple monitors still render when you're in fullscreen. So usually for multiple monitors people make sure you have extra vRAM, but 2GB has been pretty much ok for most people up until maybe last year. NOW I think the more the better, both due to lazy devs and higher resolution monitors becoming mainstream. I'd love to find me some 8GB 880MX maxwell GPUs next year .

That wasn't what I was saying. Settings obviously have the biggest effect. I'd never argue otherwise.

[D2ultima]

That wasn't what I was saying. Settings obviously have the biggest effect. I'd never argue otherwise.

The reason I double quoted you earlier was because your previous statement said he's much more likely to run out of GPU power before he runs out of vRAM. "It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI." is what you said. So I was saying it isn't so black and white. Anyway, I'm writing a full guide now; I might as well since I already did one for SLI. I do these things when I'm bored or I run into too many people who be confused so I can just be like "use the guide in my sig" or something.

[Techhog]

The reason I double quoted you earlier was because your previous statement said he's much more likely to run out of GPU power before he runs out of vRAM. "It's that you'll run out of GPU power before you run out of VRAM, which is why the 6GB 780 can be a good choice for SLI." is what you said. So I was saying it isn't so black and white. Anyway, I'm writing a full guide now; I might as well since I already did one for SLI. I do these things when I'm bored or I run into too many people who be confused so I can just be like "use the guide in my sig" or something.

Yeah, I guess I needed to say, "for the majority of games."