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Technical question on Crossfire

Last response: in Graphics & Displays
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June 12, 2011 4:56:38 AM

Hey All,

I understand the overall performance aspects of crossfire -- but I have a question about how workload is distributed between the cards. Does having two cards performing the same workload that one card is currently performing reduce the heat and strain on each of the cards respectively? Or does the second card only add capability?

My HIS sometimes sounds like vacuum cleaner under heavy load ... I am hoping that adding another wouldn't double my heat and noise ...

About me: I have a 5770. Plenty of power and room in system. Price have dropped below 100 for another and I am thinking I need to do it soon before they disappear from the market...

p.s. Has anyone tried crossfiring a 6770 with a 5770? They are essentially the same card ...

Thanks!
June 12, 2011 9:45:19 AM

adding another WILL add more heat and noise, probably won't double it though. You have another source of heat right next to the first card so things will get hotter with less air flow between the cards. The only thing you can do is add more ventilation and/or lower the ambient temp of your room with an aircon. No you cant crossfire the 6770 with 5770 unless you find a way to bios flash one or the other so the BIOS's are the same.
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June 12, 2011 5:11:13 PM

The cards are not compatible, you can go with a 5770 or 5750. It will not reduce the heat or noise. It will make it a bit worse, and much worse under load as the cards usually restrict the cooling airflow to one of the cards making the fan work harder. Does provide great power though. I used crossfired 5770's until a month ago and was very happy.
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June 12, 2011 8:20:06 PM

I appreciate the input on crossfire -- but can anyone direct me to an explanation of how the graphics workload is distributed between cards?

EDIT: p.s. shane you should tell your wife that computers are a GREAT hobby because they keep you at home being reliable instead of out carousing where there are other women...
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June 13, 2011 4:20:47 AM

Hey
I'll let you explain that to my wife. Sorry this won't be the most technical explanation. The first card does all of the work until more processing power is required at which point the 2nd card kicks in.
You don't double your memory. If you have 2 1 GB cards you don't run 2 GB of GPU memory you only still have one GB in use. The 2nd card helps render more graphic power when required. You get to use the extra shaders and stuff.
As far as your end power with 2 5770's you end up equivalent to a 5870 or 6950 in many applications. Before people start debating this...yes a single 5870 is a better solution. Thanks ahead of time for pointing this out! With 2 5770's you will be able to play pretty much anything at the top resolution with great frame rates. Except 2033. That game is optomized REALLY poorly. I have to drop to 1680 for that one.

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June 15, 2011 12:04:11 AM

Hah -- Thanks Shane this is very helpful.

Knowing that the workload concentrates on the first card makes me think that I should get a 5770 with a very good cooler, and then use my existing 5770 as the secondary. (perhaps one of the dual fan ones?)

My current HIS 5770 sounds like a vacuum cleaner sometimes and occasionally overheats and crashes my computer when playing Civ 5 at 1080p. I'm thinking that it might do a lot better as the secondary card.

(my heat issues are only on the card--my 300 illusion with 5 fans stays relatively cool--so I think internal exhaust cards are probably fine)
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June 15, 2011 2:35:19 AM

I think you should just get a better single card with better cooler if its overheating with just one card.
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June 18, 2011 5:31:18 PM

iam2thecrowe said:
No you cant crossfire the 6770 with 5770 unless you find a way to bios flash one or the other so the BIOS's are the same.


Just for the record (in case someone else comes across this thread) this answer was wrong.

A 6770 and 5770 will crossfire, provided the 6770 is in slot 1.


I do appreciate the responses though, particularly the time you guys spent answering.
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June 18, 2011 5:44:09 PM

shane799 said:
Hey
I'll let you explain that to my wife. Sorry this won't be the most technical explanation. The first card does all of the work until more processing power is required at which point the 2nd card kicks in.
You don't double your memory. If you have 2 1 GB cards you don't run 2 GB of GPU memory you only still have one GB in use. The 2nd card helps render more graphic power when required. You get to use the extra shaders and stuff.
As far as your end power with 2 5770's you end up equivalent to a 5870 or 6950 in many applications. Before people start debating this...yes a single 5870 is a better solution. Thanks ahead of time for pointing this out! With 2 5770's you will be able to play pretty much anything at the top resolution with great frame rates. Except 2033. That game is optomized REALLY poorly. I have to drop to 1680 for that one.



A couple things that need correcting here. If you have crossfire enabled and in an application that will use crossfire, crossfire is used on the 2nd card. It has nothing to do with the game needing more power than 1 card can handle, it just uses it and give you FPS beyond what your monitor can display.

If your CPU or another part of your system is holding back the ability to generate frames, both cards will have their workloads lowered. Generally they will show very close to equal loads at all times, even if at 50% workload. The same thing happens when you enable V-sync, since you cap the FPS at your refresh rate (usually 60hz).

Metro 2033, from my perspective, is optimized extremely well. Not only does the game push the limits at it's highest settings, and looks amazing, doing things no other game does with visuals, but at low settings, it does a remarkable job at loading pre-calculated routines to make a very attractive looking game even if your system can't do everything the very best systems can.

Just because a game can use and require the top of the line hardware to handle it's best settings, does not mean it's poorly optimized. It often means they add more visual levels. A good example of a REALLY poorly optimized game, would be Gothic 3. While it looks ok, it requires far more hardware requirements than games that look better.
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June 18, 2011 9:18:59 PM

Hey Bystander -- thanks.

bystander said:
If you have crossfire enabled and in an application that will use crossfire, crossfire is used on the 2nd card. It has nothing to do with the game needing more power than 1 card can handle, it just uses it and give you FPS beyond what your monitor can display.


So in a game like Civ 5, where FPS are not the issue and my GPU is crashing with all of the settings turned up high? What effect would crossfire have? Would the additional power actually make a difference?

(im running an 2500k on P8P67 delux - there are no GPU bottlenecks)
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June 18, 2011 9:33:44 PM

deadlockedworld said:
Hey Bystander -- thanks.



So in a game like Civ 5, where FPS are not the issue and my GPU is crashing with all of the settings turned up high? What effect would crossfire have? Would the additional power actually make a difference?

(im running an 2500k on P8P67 delux - there are no GPU bottlenecks)


If your CPU is holding back performance, then both cards will be used less than 100%, maybe 50% on both cards, but both cards will be used. When crossfire is enabled, it has every other frame rendered by alternating cards in most cases, in some cases it will have half the screen rendered by one, and the other half by the other.

If the CPU is not holding anything back, you'll just have a lot of FPS, more than your monitor can display.

I like to use v-sync to limit the power used when I have more power than needed.
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June 25, 2011 3:09:24 AM

Best answer selected by deadlockedworld.
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