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Underperforming 4850s

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I have 4850s running in crossfire on a Gigabyte x48 mobo. This is my first build, and I'm not quite sure what I could be doing wrong, I've been struggling with this for quite a while. 3dMark06 is rating my crossfired cards at like 5k points. Sometimes I even get a "device driver stopped responding" when I hit the 5th test. In games, my framerates are decent, but still seem like they arent as good as they should be. My psu is an antec truepower quattro 850w. Someone on newegg said it ran his rig with tons of HDDs, optical drives, and two 9800GX2s, so I can only imagine this is enough to power my system. I know I have crossfire enabled in the catalyst control center, I just have no idea why my performance is this poor. I'm also using an e8400 at stock 3GHz, so I doubt that would be bottlenecking anything.

Could the fact that my PSU supplies only 18A on its 12V rails be a problem? Would that underampage make my computer shut off, or would it just make it perform badly. I've used GPUz and the clocks are kicking up when in 3d mode to like 640MHz core and 1000MHz memory, and it runs at that load just fine. Any reason why my framerates / synthetic scores especially are so underwhelming?

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Um, I think the sm2 was like 2k, as was the sm3, and like 1k for the cpu (an e8400 for christs sake). Just ran the cards on my friends computer and they each got 11k on their own, his e6750 conroe got like 2.7k of that score, and like the other 8k was split pretty evenly between the two sm2 and sm3 scores. I think maybe 4.7k for the first score and like 3.3 for the other? anyway, way more than im getting on my rig. All the other parts have been isolated and tested.

At this point, I have either a motherboard problem or a power supply problem. My computer isn't powering off, its just not doing as well as it should. Even my cpu score is extremely low in these 3d mark tests. What. The. Hell.
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based on your CPU score I'd say it isn't running at the full speed thus crippling the sm scores as well. Make sure it is set correctly in the bios and that the cpu temperature isn't too high, ie below 70C for cores, so it isn't throttling down itself...
Get CPU-z and RealTemp to get some info out off your system...

According to CPU-z I have it set to protect against any kind of throttling, its running at 3.0GHz like it should. I just got 7k and then 7.4k on my system, like 4.1k/4.8k/1.1k for the three different scores. It seems to be doing better now, but now running crysis tests, my computer power just dies. Still not sure if it might be a cpu heat problem or compatibility or what the deal is, trying some different solutions tomorrow.

so hows the load temps? It could still be tripping the emergency shut off because of heat...

edit and I don't understand what you mean "I have it set to protect against any kind of throttling" because that throttling is a safety feature meant to protect the cpu against overheating, it lowers the clocks and voltage thus reducing the power and heat output, so it doesn't bake itself to death

Kari said:
could you tell the separate 3dmark scores you get for sm2, sm3 and cpu, that might help to identify the problem

and your psu has a total of 64 amps on the 12V rails so thats not the problem http://www.antec.com/us/productDetails.php?ProdID=27850


That's not entirely accurate. He has 4 separate 12V rails with each rated at 18A for a total of 64A (768W). Often each PCI-E conntector is on it's own rail. It is a SLI ready PSU, so more than likely this is the case. So we can assume, a single PCI-E connector would be limited to 18A (max overcurrent is probably around 20.5).

Test have shown that a fully loaded HD 4850 draws approximately 275W which is roughly 23A. That is at stock settings. Of course, a 4850 is not typically "fully loaded".

http://www.theinquirer.net/gb/inquirer/news/2008/06/26/...


^^well son, you just missquoted your source, that 267W is for the ENTIRE system. They did some math and came up with a 134W for the card itself, which is more plausible since the card has one 6 pin pcie power connector that can supply around 75W and the slot itself another 75W...



You are correct I did misread the table but I have also seen two other reviews that state a 4850 uses roughly 250W and a 4870 275W+.

One of them also compared the power draw to other major cards.

Perhaps I misunderstood the others.

I'll see if I can dig those up as well and verify it.

At any rate, my point was more to the fact that he does not necessarily have 64A on his 12V rail.

After going back and reading a half dozen or so reviews again. Some state total system power and some only mention the numbers as "the cards power consumption".

A couple have actually added notes that the power consumption is for total system power.

gmanvbva said:
At any rate, my point was more to the fact that he does not necessarily have 64A on his 12V rail.
hmm well yes...
but the way those craphics cards are designed, if they need tons of power there will be tons of pcie power connectors as well. The atx standard specifies the max current of a single rail somewhere around 18 or 20 amps, forget which one it is and don't have the specs right now, and that has been taken into account when those craphics cards were been designed (and most of the PSUs). So really PSUs with big single rail aren't really following the standards but since they work just as well or even better in some OC occasions, they are sometimes viewed as better alternative.

The confusion comes in because you really have no idea how those 12V rails are divided amongst the various connectors.

The SLI requirements call for both PCI-E connectors to be on separate rails, so if you have a SLI certified PSU, you at least know that.

I think this should be in the manuals at a very minimum. It would help solve a great deal of issues and provide a little better guidance how to connect your components in a more balanced fashion.

Here is what the ATX Rev 2.2 states with regards to the 12V rails.

1.2.1. Increased +12 VDC output capability
System components that use 12V are continuing to increase in power. In cases where
expected current requirements is greater than 18A a second 12 V rail should be made
available. ATX12V power supplies should be designed to accommodate these increased
+12 VDC currents.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_...

Here is another document on PCI Express Power Requirements.

http://www.maxim-ic.com/appnotes.cfm/an_pk/3605

"The new maximum power levels supported by this specification are 25W (low-profile card), 75W (standard size), and 150W."

A PCI Express x16 Graphics 150W-ATX add-in card can draw a maximum of 75W through the standard connector, as specified in PCI Express CEM 1.1. Up to 75W additional power is provided through a 6-pin wire-to-board connector. Therefore, the maximum total power that must be provided to a PCI Express x16 Graphics 150W-ATX add-in card is 150W.

A PCI Express x16 Graphics 150W-ATX add-in card must adhere to strict power-distribution, power-up, and power-consumption requirements. To ensure safe operation and compatibility with noncompliant installations, the following power-management requirements must be met:

* The +12V delivered from the standard x16 connector and the additional +12V delivered from the dedicated 6-pin power-supply connector must be treated as coming from two separate system power-supply rails.

A little bit off the original topic but worth mentioning is the only requirements with regards to current limits are on the 12V rail supplying power to the motherboard.

So even though there could be 4 12V rails rated at 18 A, the overcurrent limit could be imposed differently for each rail and two (or more) rails could be combined for overcurrent conditions..

This is why you will see some diagrams group 12V rails for wattage/overcurrent conditions.


"1.2.3. Separate current limit for 12V2 on the 2x2 connector:
The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet
the requirements of UL and EN 60950."

BTW, I feel 134W is dangerously close to the 150W maximum draw (75W from PCI-E bus and 75W from the PCI-E connector) since these are at stock settings. I would be curious to see if anyone has tested the power draw when they are overclocked.

Then again, they say to take off ~20% due to the PSU's inefficiency. So that probably makes up for any added power requirements from overclocking.

yeah that too, and when you do some more math it becomes quite clear that those numbers are still somewhat of an estimate. If you try to calculate the power usage of the rest of the system you get numbers varying between 109 W and 142 W. Of course thats only derived from a 3dmark run and thus it might not stress the whole of the system up to 100% with every card tested.
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