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SLi Vs. non-SLi


wook

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When buying a laptop there are always many questions we want answers to... And unless you have direct experience then you usually make the purchase, and find out the hard way. One of the topics for discussion is SLi and non-SLi systems.

sli_logo.jpg

I had researched this before I purchased my SLi system, and could not find a performance comparison. So though I?d offer it here if anyone is interested. Plus it will give an indication how the two perform.

8700m GT - SLi

In a test with my 8700m GT the system achieved 24 Fps. The same test with SLi enabled the system scored 36FPS.

Now like most of us, I knew that SLi would not double the performance of the base card in the unit. But these results show a good improvement over all.

The same test with an 8000m GTX card was 40 FPS. (I would expect the 9800 GTX to score slightly higher than this)

SLi also uses 20-50% (possibly a lot more) more processing power depending on the game played. Example Crysis utilises SLi very well, where as Mass Effect used a constant 80-95% of the processing power of my laptop. (Core2 extreme 3.0 GHz) I actually got better performance disabling SLi with this game.

(Smoothness and FPS combined)

It's also interesting to see what kind of power consumption SLi systems have. Obviously this will differ on each system, but using two GPU's as opposed to one should use twice as much power. Anyway this is what i found:

Battery mode: non-SLi 108 mins. (29 Watt)

Battery mode: SLi - 43 mins (58 Watt)

Thats 40% more power consumption using SLi. Hungry little sucker!

(This was just a simple *.avi play back test)

Hope this simple post will help prospective buyers purchasing SLi or not.

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Nice work! :) I'm quite sure this will be of great help to the numerous buyers who believe that SLI will double their performance and increase performance in all circumstances.

Also, this reminds me of people (like me at one point) that would believe that a 9300m is better than an 8800m gtx before they purchase.

This is a good way of letting people know what to expect from SLI.

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CHeers Andrew. last year i thought SLi would be twice as fast.

mmm.. good point Claw. i'll do a battery test and see what happens. cheer!

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2 GPU's does most certainly not mean 2x performance but does mean 2x power use.

I would expect about 10% increase in performance.

SLi = bragging rights at LAN parties ? but first to have to plug in :)

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Greetings friends,

On this topic I'd have to add I'm running an SLi laptop, XPS m1730 with 2x 8800m GTX in SLi

As for the performance increase comparing series 8 and 9, this will virtually be non-existent, the clocks and stats are virtually the same on the GPUs/mem/shaders... the biggest "difference" is the fact that the 9800m GTX usually comes with 1GB mem. More memory isn't always more performance... in fact more often it's not. 1GB dedicated memory per gpu looks interesting and flashy, but if your GPU cannot utilize it all (which is the case in most GPUs atm) then you are screwed nonetheless. (read performance drop instead of increase in performance)

There are three things that could hold you back from buying an SLi laptop:

1: The price

2: The lack of driver support

3: The fact that not all games utilize SLi yet and SLi is not a fully matured system yet, meaning that even with the latest drivers you cannot take the maximum advantage of having the technology at your disposal.

Other than that I have to add that my laptop outraces quite a lot of desktops, so if you do have the money and mobility or space are your primary concerns....but you still want a powerhouse that can even be overclocked very nicely ... then maybe you should think about it,..... for everyone else: buy a freaking desktop.... you'll get something faster for half/a third or even a quarter of the money in some cases.

My 2 cents...

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also forgetting the next generation of GPU. There are quite a few added anhancments for DX10

The 9800M GT is slightly faster than 8800M GTX. about 2-3 fps in Crysis.

So when/if the 9800m GTX comes out, and in sli... it would be quite a bit better than the 8800m GTX in SLi. 8-10 FPS probably.

also considering the memory increase. this wont affect speed like you mentioned, but will make the performance better. especially compairing the smoothness of FPS games that buffer game physics and resources.

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For your consideration:

What is VRAM?

VRAM is Video RAM. It's memory that resides on the graphics card and is dedicated for the card's use. It is often faster than regular system memory, and more importantly, its close proximity to the graphics processing unit (GPU) on the graphics card allows for quick access to data stored in this memory for rendering graphics scenes.

What is it used for?

It's used for any data that the graphics card needs to render a scene in a game: vertex data for models, textures, shader textures, a buffer for the pixel data that will be sent to the monitor.

So is more better?

Up to a point, yes. (UP TO A POINT, meaning only on the highest resolutions and only if your GPU can handle the amount of memory on the card, which once again is not the case in most GPUs on the market today I do not know about the 9800m GT or GTX, but even a 8800GT with 1GB of VRAM has too much memory to handle and will actully not improve in scores even though the amount of VRAM is double that of most competing 8800 series cards.) The general rule of thumb with RAM of any sort is that you will see an improvement up until you have enough, then there will be no improvement after that. This is because data stored in the VRAM is able to be quickly accessed by the GPU, while it takes longer to access the same data from main memory. If there's not enough room for all the data it needs in the VRAM, then it needs to store part of it in the computers main RAM, which takes longer to retrieve, and therefore slows down rendering times while the GPU waits for the extra data. So unlike a processor, where more speed is almost always an improvement, adding more RAM only helps until you've got enough to hold the data you need, and the rest is just wasted space.

Will more VRAM improve my framerates?

Maybe. It depends on the situation. More VRAM does not make the GPU process graphics data any faster, only access it faster when it needs it. So if you're trying to run a game at a high resolution like 1920x1200, that means that in the end, the GPU has to process 2,304,000 pixels, and the speed it can do that is ultimately limited by the capability of the GPU chip, and not by the amount of VRAM it has available. If the GPU is too slow to run a game at the resolution you're running it at, more RAM won't help.

However, since VRAM size determines the amount of data stored locally to the GPU, it will affect how much data can be involved and still run at the same speed. So you can use higher quality textures, more anti-aliasing, and more shaders (which are stored as images, similar to textures) at the same resolution and still get a good framerate because the card can hold all that data locally, and doesn't have to wait to fetch it from the main RAM. It's worth noting that the pixel buffer is stored in the VRAM - a higher resolution will increase the size of the buffer, which could then push other data out to the main memory.

So how come my card with (e.g.)128Mb doesn't run this game well!? It's an 128Mb card, and the requirements for the game are only (16/32/64/whatever)Mb!?

See the above answer. It most likely because the card in question pairs a slower or less capable GPU with a lot of memory. If the GPU is too slow to process everything going on in the game, then it doesn't matter that it has lots of memory. The main reason why this tends to happen is because the graphics card makers have lots of different models for any given generation, all of which have different capability. Add to this the fact that cards of different generations are available at any given time, and it can be confusing for people trying to figure out which card is the best to buy, or whether their card is as good as the one listed on the game box. Because of this, they quite often use 'graphics card with x-Mb VRAM' as a requirement for a game, or feature the amount of memory prominently on the box for a graphics card. In theory, because the amount of memory has been going up with each generation of graphics cards, this gives you a general idea of the capability of a card, but it's problematic.

The amount of memory on the card actually gives no idea what the capability of the GPU on that card is.

To make matters more confusing, the graphics card makers will sometimes re-release an older GPU with more VRAM as a new card.

So how do I figure out what a good graphics card to buy is? / How can I figure out if my graphics card can run a game?

Instead of looking at the VRAM, look at the model number. There are lots of them, but in general you have the generation of video card, followed by the class of card, usually followed by a suffix. It can get confusing - but the model number gives a better general idea of capability. For example, the current (as of this writing) generation of nVidia cards are numbered as such: 8800, 8600, 8500, with the '88' series being the high-end, '86' as the mid-range, and lower than that as budget cards. The previous generation was similar: 7800, 7600, etc. Usually between generations of GPU, they come out with new cards that are using the same GPU, but running at a faster speed, for example, the 7900 series in between the 7800 and the 8800. It's expected that a 'refresh' of the current generation will be released with a similar naming scheme.

So naturally the 9 series will be better, but in this case the 9 series are just slightly improved 8 series cards and chips.... it's well known that the 9 series are not exactly a worthy successor of the 8 series as the performance jump only gets significant if you look at the X2 series and such.

No offense intended by any of this ....

Just another few cents

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quite right. 7000 series to 8000 series was a good jump. but 8-9000 was pretty strandard, as both 8 and 9 series chips are pretty much considered the same in game recomendations and performance charts hardly differ

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