crossfirex A second 7870 Tahihi worth it?

[Elliot B.]

I currently have:

• Antec Earthwatts 500W PSU
• 3750K CPU
• ASRock H77M motherboard
• Radeon 7870 Tahiti LE GPU

I'm tempted to get a second 7870 Tahiti LE.

 

I know I'll need to upgrade my PSU (to 650W+ as I have many HDDs, plus one that supports CFX).

 

So, provided my PSU is ready, should I get a second 7870 Tahihi LE?

 

Have AMD fixed their CFX problems? (I heard something aobut unstable frames due to syncing or something?)

 

I've seen in some general CFX benchmarks that some games etc. utlise 100% of the second card. Does that mean, as long as the CPU is capable, that the framerates will double that of a single card?

 

Talking of a capable CPU, would my 3750K suffice?

 

Finally, my motherboard only supports 1x x16. The other slot is an x4, which means I believe both cards would run at x4. Would this be a huge issue? Would I need a new motherboard that supports 2x x8 (or 2x x16) to make 2x 7870 Tahiti LE worth it?

[psionicinversion]

It could be worth it yeah and a i think there newest drivers have tried to really minimize the frame pacing issue, if thats what its called. Having a xfire/sli config youll never see 100% extra performance maybe 70-80% extra although i think the new 290's arent to far off with the solution built directly into the GPU.

 

Hmm i thought it would support it but i dont think it does actually, says quad xfire but think youll get really low speeds so its not worth it. So youll either have to get a new MB or buy a new GPU

[threetonesun]

In my opinion, it's almost always better to sell the card you have and use that money towards buying a newer single GPU than going with an SLI / Crossfire setup. There are a few good reasons to do dual GPUs:

• You just bought two of the most powerful cards currently on the market, and there is no single GPU solution faster.
• Your current GPU is fairly old and a second one can be picked up for dirt cheap.
• You can use your old card as a Physx processor or for some other calculations alongside an unrelated newer card.

The downsides to Crossfire: it's definitely not a 100% increase in framerates, some games won't support the second card at all, it requires more power and generates more heat than a single GPU, you have to have a motherboard that supports it. Yours does, BTW, and the 4x slot would not be an issue.

[Elliot B.]

Do I install it by just plugging it into the second port (and PSU connector of course)? Do I need a bridge or anything?

How will I know if a game is using the second card?

How do I make sure the latest CFX "profiles" are installed - just by installing the latest Catalyst drivers?

[Andre S. Veteran]

1) Yes you need a crossfire bridge. You might have got one with your motherboard if it supports crossfire. Otherwise you can buy it separately. 

 

2) Games don't decide if they use crossfire or not, your driver does. If you configure the driver to use crossfire, all games will use crossfire.

 

3) Yes the profiles come with the drivers. You don't have to do anything special.

 

That said, for the price of a new PSU + 200$ for the new card, have you evaluated if there wasn't any worthy single-card alternative? Running two cards does come with its set of issues: increased noise and heat output for one thing. The performance gain is also not always consistent depending on titles, and there's slightly more frame latency (due to the nature of alternate frame rendering).