3 gb and 2 gb vid card in SLI

[hodgenutts]

Question, If I have a 3 gb card in one slot and a 2gb card in another, would I get the vram performance of the 3 gb card? The reason I ask is that it is my understanding that the vram of the second card is not used in SLI

 

[netzz3d]

no it would only use 2gb

 

[lavaheadache]

what card comes in a 3gb and 2gb variant?

 

[MentalIlness]

GTX 660 / GTX 660 Ti

 

[hodgenutts]

Ok, I'm confused, if it doesn't use the vram of the second card and the first card is 3gb, then why would it only use 2gb? Is this your opinion or do you actually know for sure. Just doesn't make much sense that the vram of the second card isn't used and if your first card is 3gb, then why would it only use 3 gb of vram?

 

[lavaheadache]

Sli and crossfire will mirror the lowest common denominator when it comes to Vram. Both cards need to have the same information as they are working on the same workload. the ram doesn't add up.

 

[Keromyaou]

Are you sure that gtx 660 ti and gtx 660 work together as sli? As far as I know, Nvidia cards are very strict about the graphic cards used for sli. This is from Wikipedia;

CrossFire can be implemented with varying-GPU cards of the same generation (this is in contrast to Nvidia's SLI, which generally only works if all cards have the same GPU). This allows buyers who have varying budgets over time to purchase different cards and still get the benefits of increased performance. With the latest generation cards, they will only crossfire with other cards in their sub series. For example, GPU in the same series can be crossfired with each other. So a 5800 series GPU (e.g. a 5830) can run together with another 5800 series GPU (e.g. 5870). However GPUs not in the same hundred series cannot be crossfired successfully (e.g. a 5770 cannot run with a 5870).

Frankly I don't think that gtx 660 and gtx 660 ti doesn't work together.

What lavaheadache said is correct as far as I know. For example if you do sli with gt9800 1GB and gt9800 512MB, you can only use 512MB as vRAM.

 

[BrightCandle]

I didn't think you could sli a 660 and a 660ti.

In principle the way to think about SLI is that every card in parallel gets all the information about the world and its textures and runs the shader programs. Each card works on different frames and hence if you were to have a card in SLI with additional memory you wouldn't be able to utilise more than the minimum because otherwise the card with less would be considerably slower and many of your frames would be a mess.

For this reason SLI does not support mixing cards that aren't basically the same whereas AMD does allow quite a lot more wiggle room, although its rarely a good idea.

 

[hodgenutts]

I wasn't talking about sli'ing a 660 gtx and and a 660ti, I meant
Sli'ing a 3gb gtx 660 (non ti) with a gtx 660 2gb (non ti). Sorry for the confusion. I asked because I read somewhere that for some reason the 3gb scales better with the 192 bit bus controller...

 

[moonbogg]

I wouldnt try it personally as I would expect problems, but who knows, it might work.

 

[Face2Face]

It should work perfectly fine. But as others have said both cards will only utilize 2GB of vram each.

 

[Eureka]

I wasn't talking about sli'ing a 660 gtx and and a 660ti, I meant
Sli'ing a 3gb gtx 660 (non ti) with a gtx 660 2gb (non ti). Sorry for the confusion. I asked because I read somewhere that for some reason the 3gb scales better with the 192 bit bus controller...

You're still going to use 2GB. Remember that both cards are supposed to mirror each other, so it copies the same data onto both cards.

It's like trying to copy a 150 page notebook onto a 100 page notebook.. you're going to run out of pages.

 

[moonbogg]

You're still going to use 2GB. Remember that both cards are supposed to mirror each other, so it copies the same data onto both cards.

It's like trying to copy a 150 page notebook onto a 100 page notebook.. you're going to run out of pages.

That would be my concern. How do you know which card the driver will consider primary? What happens when it tries to use over 2gigs of ram?

 

[Lonyo]

That would be my concern. How do you know which card the driver will consider primary? What happens when it tries to use over 2gigs of ram?

The one with least RAM.
It picks the lowest common denominator.
e.g. if two cards have different clocks, it would usually pick the lower clocks (I don't know if they changed this and enabled asynchronous clockspeeds, but in the past it was the lower speeds), same if cards have different amounts of RAM.

 

[crisium]

I read somewhere that for some reason the 3gb scales better with the 192 bit bus controller...

From Tom's Hardware comparing multiple GTX 660 Ti's, many 2GB versions and 1 3GB version, the 3GB card was downright slower. I'd check more reviews, but personally I wouldn't dare get a 3GB 660 if even a 660 Ti 3GB can't handle the VRAM.

 

[KentState]

Just like RAID 0, you get twice the performance, but limited to the lowest common denominator.

 

[hodgenutts]

LoL well I can't even get SLI to work with the same exact 2 cards lol, the option for SLI doesn't show up in invidia control panel