Help me understand crossfire

[jhansman]

Apparently most Radeon cards need a physical bridge when using two or more in concert, but most of those I see pictured don't seem to have a connector on top, so I'm a bit puzzled. Can someone explain to me how these cards work. TIA.

 

[jhansman]

Really? Nearly 60 views and no one can answer this question? C'mon guys, I know there's someone out there who has the answer.

 

[dawp]

what price point were you looking at? afaIk, all crossfire compatible cards have the bridge connector on the top edge of the card.

this one has them:

http://www.newegg.com/Product/Produc...82E16814131434

as does this one:

http://www.newegg.com/Product/Produc...82E16814102918

this one doesn't:

http://www.newegg.com/Product/Produc...82E16814131441

 

[wand3r3r]

Apparently most Radeon cards need a physical bridge when using two or more in concert, but most of those I see pictured don't seem to have a connector on top, so I'm a bit puzzled. Can someone explain to me how these cards work. TIA.

Yes, that is correct, they do need a physical connection to connect the cards. This is the crossfire bridge. http://www.newegg.com/Product/Produc...82E16814999002

This is how they connect.

The connector itself is on the top of the card like this

Using crossfire is as simple as buying 2 compatible cards and connecting them with that crossfire bridge. The cards have to be similar, e.g. from the same series but there is some variability. For example 2 HD6950's are certainly compatible, even if the memory amount is different, but they are limited to the lower card's specifications (memory size, gpu).

I know you could mix and match somewhat so I believe a HD6870 and HD6850 could be used in crossfire but both would be limited to the limitations of the HD6850 so you'd lose the extra power that the HD6870 has over a HD6850. I don't think a HD69XX would be compatible with the HD68XX and certainly not with a HD67XX. (correct me if I'm wrong as I'm not 100% sure about the mixing and matching.) Either way there is no point to crossfiring a 67XX with a 69XX because 67XX in crossfire probably doesn't have gains over the 69XX.

Anyways if you are thinking about going crossfire, check the benchmarks on your card crossfired on the games you play because the gains vary and some games don't benefit as much as others. Some scale quite well though so it's usually a cheaper upgrade than buying the next class of cards if you already own own card.

 

[jhansman]

OK, so far, so good. My confusion stems from the fact that this card is listed as having "CrossfireX support" but shows no such connector:

http://www.newegg.com/Product/Produc...82E16814103191

Is this an error in the product listing, or am I having vision problems? At any rate, thanks for clarifying this.

 

[ShadowVVL]

yeah that is pretty confusing, i would assume no CF on that card but i dont own any radeons.

 

[Cuular]

Some of the lower end cards just use the PCIe bus, since the amount of data needing to be sent isn't that much. That card qualifies as a low end card.

 

[apoppin]

OK, so far, so good. My confusion stems from the fact that this card is listed as having "CrossfireX support" but shows no such connector:

http://www.newegg.com/Product/Produc...82E16814103191

Is this an error in the product listing, or am I having vision problems? At any rate, thanks for clarifying this.

Cuular is correct. The lower-end Radeons do not need a CrossFire Interconnect Bridge.

What do you want to understand about Crossfire?

 

[jhansman]

Cuular is correct. The lower-end Radeons do not need a CrossFire Interconnect Bridge.

Right. Further investigation tells me that some 6670s have connectors, but most don't, as (apparently) two of these GPUs bridged are probably not as potent as a single 6770 or higher card. Then then leads me to my second question: at what point does it make sense to couple (or triple) these cards vs. a single GPU with more muscle?

 

[apoppin]

The Diamond card I linked above is a 6670. According to this chart:

http://sites.amd.com/PublishingImag.../WebBannerJPEG/AMD_CrossfireX_Chart_1618W.jpg

a 6670 card needs a bridge for Crossfire functionality. Yet, that Diamond card has no bridge connector; hence, my confusion. Yes, most of the pics of >5570 Crossfire cards on Newegg show the requisite connectors, so I can't quite figure out why the Diamond card would not. Also, are you saying that 6670 cards are considered the 'lower end'?

According to the AMD reviewer's guide, an Interconnect Bridge is unnecessary for HD 6670. Yes it is low end (think, HD 6970; or HD 6990 at $750) i can't link to my own review here, but this one will do:
http://www.hardwarecanucks.com/foru...adeon-hd-6670-1gb-hd-6570-512mb-review-4.html

One item that seems to be missing from these cards is the usual Crossfire connector which is used to bridge a pair of more of AMD cards together. This is because lower-end AMD cards have the ability to reserve part of the PCI-E bus for the Crossfire interconnect so in effect, two lower end cards can work together for increased performance but scaling will likely be affected. In addition, due to their low power consumption needs neither uses an auxiliary 6-pin PCI-E power connector.

Some of AMD's partners may offer a 6670 with an interconnect bridge; if you must have a 6670, get that one.

HD 6670 CrossFire is really weak. You'd do a lot better buying a single card if you are interested in gaming performance unless you already have a HD 6670.

 

[cjtodd23]

I think that card can just be Crossfired with a motherboard's integrated graphics, right? Maybe with the graphics on a Brazos or Llano board too?

 

[jhansman]

HD 6670 CrossFire is really weak. You'd do a lot better buying a single card if you are interested in gaming performance unless you already have a HD 6670.

Makes sense. What would you recommend? No budget as yet, just lookin'.

 

[Seero]

Cfx or sli, the principle is the same, to scale up performance. Although single card solution is always better than multi, you can always get similar performance at fraction of the price. The other extreme is if the best card is not enough, then you get several of them and slightly or CFx them.

Pcie acts like a media for communication. It isn't the bandwidth that is lacking, but the overhead on it. In layman terms, the bridge acts like an express medium between two cards without the overhead as the relation is one to one. Since the cards don't work independently. This express medium is mandatory to unleash the full potential of scaling. Remember, unless the single card solution is too expensive or lacking, you really don't want to go multi.

 

[apoppin]

Makes sense. What would you recommend? No budget as yet, just lookin'.

It depends on your budget.

Why do you want to CrossFire your cards?

 

[3DVagabond]

If your budget is ~$200.00, the price of 2 of those 6670's, then you can get either the AMD HD6870 or nVidia GTX560 (not to be confused with the GTX560ti which is a dearer card). Both would be less after rebates, but before rebate they are both ~$200.00 and below.

 

[onethreehill]

According to the AMD reviewer's guide, an Interconnect Bridge is unnecessary for HD 6670. Yes it is low end (think, HD 6790; or HD 6990 at $750) i can't link to my own review here, but this one will do: snip

Do you mean to type HD 6970?

 

[apoppin]

Do you mean to type HD 6970?

Yes. Typo

Speaking of the HD 6990, mine appears to have failed. It artifacts at stock speeds even on the desktop

i wonder if AMD will send me a replacement - it has been mildly overclocked
:whiste:

 

[Carmen813]

Yes, that is correct, they do need a physical connection to connect the cards. This is the crossfire bridge. http://www.newegg.com/Product/Produc...82E16814999002

This is how they connect.

The connector itself is on the top of the card like this

Using crossfire is as simple as buying 2 compatible cards and connecting them with that crossfire bridge. The cards have to be similar, e.g. from the same series but there is some variability. For example 2 HD6950's are certainly compatible, even if the memory amount is different, but they are limited to the lower card's specifications (memory size, gpu).

I know you could mix and match somewhat so I believe a HD6870 and HD6850 could be used in crossfire but both would be limited to the limitations of the HD6850 so you'd lose the extra power that the HD6870 has over a HD6850. I don't think a HD69XX would be compatible with the HD68XX and certainly not with a HD67XX. (correct me if I'm wrong as I'm not 100% sure about the mixing and matching.) Either way there is no point to crossfiring a 67XX with a 69XX because 67XX in crossfire probably doesn't have gains over the 69XX.

Anyways if you are thinking about going crossfire, check the benchmarks on your card crossfired on the games you play because the gains vary and some games don't benefit as much as others. Some scale quite well though so it's usually a cheaper upgrade than buying the next class of cards if you already own own card.

This is incorrect, you are no longer limited to the slower cards performance. This was fixed some time ago.

 

[wand3r3r]

This is incorrect, you are no longer limited to the slower cards performance. This was fixed some time ago.

What about memory? If you had e.g. 1GB on 1 card and 512MB on the other I believe it was that the card with the larger memory could only use half?

 

[jhansman]

Why do you want to CrossFire your cards?

Not so much that I want to, just that the mobo in my upcoming build supports it, so I wanted to see what the deal was. From what I can glean from this thread, a more powerful, single card will probably give more bang per buck. My current card is fairly weak and aging, so I just want to make my next GPU move carefully, with as much info as is useful.

 

[apoppin]

CrossFire or SLI is a great option to have and it is worth considering when you are buying a video card. What you should buy always depends on the timing of your build and on your budget considering your needs and the resolution you play games at.

 

[Carmen813]

What about memory? If you had e.g. 1GB on 1 card and 512MB on the other I believe it was that the card with the larger memory could only use half?

hmm, that I don't know. However I know the clocks are not an issue. I use a 5870 + 5850 and they run at separate clocks.