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Old Dec 13, 2012, 10:58 PM   #1
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Not going to respond to spurious nonsense in this thread.

I think that's why revel started his own thread to "confirm" our findings. Let his be the one with spurious nonsense.

7950 works great.

If it has 2 @ 6 PIN PLUGS, GREAT, THAT'S EXACTLY WHAT THE MAC PRO IS DESIGNED TO DELIVER.

PROBLEM SOLVED, NONSENSE AVERTED !!!
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Old Dec 14, 2012, 10:29 AM   #2
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Not going to respond to spurious nonsense in this thread.

I think that's why revel started his own thread to "confirm" our findings. Let his be the one with spurious nonsense.

7950 works great.

If it has 2 @ 6 PIN PLUGS, GREAT, THAT'S EXACTLY WHAT THE MAC PRO IS DESIGNED TO DELIVER.

PROBLEM SOLVED, NONSENSE AVERTED !!!
I'm sorry, how is that nonsense? I asked a genuine question that I thought perhaps a Video Card vendor might be able to answer for me.

If 7950's with 2x6-pin work great, will a 7950 with 6+8-pin connectors work just as great?
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Old Dec 14, 2012, 12:54 PM   #3
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I'm sorry, how is that nonsense? I asked a genuine question that I thought perhaps a Video Card vendor might be able to answer for me.

If 7950's with 2x6-pin work great, will a 7950 with 6+8-pin connectors work just as great?
Pretty sure hey gave you a great answer. I will reiterate what he said below.

I wouldn't recommend running a card that has a 6+8 pin connector. There is another thread about this and people blow the rails from drawing to much power. Stick with any card that has 6+6.
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Old Dec 14, 2012, 01:19 PM   #4
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I'm sorry, how is that nonsense? I asked a genuine question that I thought perhaps a Video Card vendor might be able to answer for me.

If 7950's with 2x6-pin work great, will a 7950 with 6+8-pin connectors work just as great?
My assumption is that the card manufacturer did not employ chimpanzees and then installed 8 pin connectors for a giggle. If they felt that a 6+8 pin connectors were necessary, then it's best to go with that.

It's kind of like when a car manufacturer tells you to use a fuel with a certain minimum octane rating. If you fill up with lower octane, because it will save a bit of money, then the car won't blow up the first time, but it will probably be pinging under hard acceleration and that equates to bad times for the engine eventually.

Unless the engineers all got stoned on the day when they were designing the card.
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Old Dec 14, 2012, 01:40 PM   #5
darkcoupon
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So you're saying a card that's only able to draw 200w Max will damage my system just because one of the connectors has two more grounds than the other one?

So the power draw diagram looks like this?

8-pin connector = 150w
6-pin connector = 25w
PCIe Slot = 25w

Makes total sense.
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Old Dec 14, 2012, 01:47 PM   #6
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So you're saying a card that's only able to draw 200w Max will damage my system just because one of the connectors has two more grounds than the other one?

So the power draw diagram looks like this?

8-pin connector = 150w
6-pin connector = 25w
PCIe Slot = 25w

Makes total sense.
No, it does not make sense when you put it like this. What I am saying is that the engineers felt that there might be situations where the card would need more than 2 x 6 pin connectors are able to provide.

Or maybe they were stoned and should be replaced with MR readers.
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Old Dec 14, 2012, 01:57 PM   #7
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No, it does not make sense when you put it like this. What I am saying is that the engineers felt that there might be situations where the card would need more than 2 x 6 pin connectors are able to provide.

Or maybe they were stoned and should be replaced with MR readers.
Yes, situations where users are overclocking, which is not possible in an OSX environment and is just plain stupid to do with a Mac Pro running windows with any card. So to answer my own question, 6 to 8-pin adapters don't ruin the system as long as the Max TDP is within spec and you're not overclocking.

Or maybe the engineers aren't stoners and the company uses 8-pin connectors anyway because they believe it's a better selling point to users who want to overclock even though they are completely useless. Marketing trumps engineering in almost all aspects of business.
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Old Dec 14, 2012, 02:04 PM   #8
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Or maybe the engineers aren't stoners and the company uses 8-pin connectors anyway because they believe it's a better selling point to users who want to overclock even though they are completely useless. Marketing trumps engineering in almost all aspects of business.
Yes, or it could be that they had already placed a large order for 8 pin connectors and figured they would use them.
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Old Dec 14, 2012, 02:39 PM   #9
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The HD7970 was leaked in December of last year with a TDP of 210w. The prototypes had 1x 6pin + 1x 8pin but was shown running with only 2x 6pin. AMD put in the 8pin because of PowerTune. The HD7970 has a PowerTune set limit of 250w. Going over that means the card will attempt to throttle itself. It doesn't mean the card strictly needs 8pin but it is there for people who 1) overclocks or 2) runs Furmark to keep their house warm. Not to mention the top end ATI and Nvidia cards has always had 8 pin connector despite the recent trend towards lower power consumption. This is also why the HD7970 GHZ has the same max tdp when logically it should use more power. It too has the same PowerTune limit.

The valid concern regarding 8 pin is not whether it is necessary or not (current gen it really is not). But the presence of 1x 8 pin makes it inherently riskier than 2x 6pin even when the power consumption is identical. Why? Because all the 8 pin does is provide 2 grounds that tell the card "hey you can draw 150w from this". So with an 6 pin to 8 pin adapter even though you still have 2x 6 pin PCI-E cables, the load will not be balanced as would if 2x 6 pin is on the card. So, get a normal clocked 2x 8 pin card...
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Old Dec 14, 2012, 02:41 PM   #10
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My assumption is that the card manufacturer did not employ chimpanzees and then installed 8 pin connectors for a giggle. If they felt that a 6+8 pin connectors were necessary, then it's best to go with that.
Unfortunately it is becoming clear that some cards have an 8-pin connector as a marketing strategy for enthusiasts and overclockers who think the card will be faster if it has an 8-pin power connector.

To further your car analogy, it's like fake exhaust tips on a car. They imply the car has more power, but it really doesn't. The engineers didn't add those; the marketing people did.

2x6 is definitely safe. 1x6 + 1x8 is not definitely unsafe; it depends on the TDP of the card.
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Old Dec 14, 2012, 03:42 PM   #11
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Originally Posted by lixuelai View Post
The valid concern regarding 8 pin is not whether it is necessary or not (current gen it really is not). But the presence of 1x 8 pin makes it inherently riskier than 2x 6pin even when the power consumption is identical. Why? Because all the 8 pin does is provide 2 grounds that tell the card "hey you can draw 150w from this". So with an 6 pin to 8 pin adapter even though you still have 2x 6 pin PCI-E cables, the load will not be balanced as would if 2x 6 pin is on the card. So, get a normal clocked 2x 8 pin card...
This is an old thread on the same issue, but here's a quote from the OP:

Quote:
But some cards have a 8 pin hole instead. Some people have reported that using a 6 pin cable in the 8 pin hole still works fine.
I don't know how viable that actually is, but it sounds like using the 6pin male in the 8pin female could merely exclude the two grounds from being detected.

Obviously it would be easier to just get a card with 2x 6-pins, but there are people out there who want the high end cards that may only be offered with 8-pin connectors (7970) and there is evidence supporting theories that the Mac Pro's logic board is able to supply more than 225w power.
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Old Dec 14, 2012, 04:02 PM   #12
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It seems like you are fishing for the answer you want to hear, and not the one being given. If your question was solved with hard evidence someone would have spoken up already. All you can deduce so far is that 2x6 is safe, and 6+8 is potentially unsafe. That's where things stand. You can postulate till the end of time (7days) but until someone does it there's no hard answer.
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Old Dec 14, 2012, 04:30 PM   #13
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It seems like you are fishing for the answer you want to hear, and not the one being given. If your question was solved with hard evidence someone would have spoken up already. All you can deduce so far is that 2x6 is safe, and 6+8 is potentially unsafe. That's where things stand. You can postulate till the end of time (7days) but until someone does it there's no hard answer.
But people are doing it

I'm not fishing for answers, I just want a solid argument from the people who say 6+8 is always unsafe and so far lixuelai has been the only one to step in with any real answers.

It just seems to be a running theme on these boards that people instantly shutdown the idea of using certain cards because they have an 8-pin adapter without looking at the actual power that the card is capable of drawing or where that power is coming from. This discussion could be very valuable to future users no matter what the result, so I don't see the point of trying to shut it down by saying "just do what we already know is safe"
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Old Dec 14, 2012, 07:31 PM   #14
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In order to get a solid answer we should look for a way to measure the resistance of the traces on the logic board.
If it's less than 50 Milliohms they should not have a problems handling 10 amps... As long as the PSU is not limiting of course.
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Old Dec 14, 2012, 07:35 PM   #15
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But people are doing it

I'm not fishing for answers, I just want a solid argument from the people who say 6+8 is always unsafe and so far lixuelai has been the only one to step in with any real answers.

It just seems to be a running theme on these boards that people instantly shutdown the idea of using certain cards because they have an 8-pin adapter without looking at the actual power that the card is capable of drawing or where that power is coming from. This discussion could be very valuable to future users no matter what the result, so I don't see the point of trying to shut it down by saying "just do what we already know is safe"
I suggest you purchase the card and necessary adaptors and run it. Report back with your results.
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Old Dec 14, 2012, 07:36 PM   #16
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I suggest you purchase the card and necessary adaptors and run it. Report back with your results.
I suggest you contribute something.
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Old Dec 14, 2012, 07:42 PM   #17
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Originally Posted by darkcoupon View Post
But people are doing it

I'm not fishing for answers, I just want a solid argument from the people who say 6+8 is always unsafe and so far lixuelai has been the only one to step in with any real answers.

It just seems to be a running theme on these boards that people instantly shutdown the idea of using certain cards because they have an 8-pin adapter without looking at the actual power that the card is capable of drawing or where that power is coming from. This discussion could be very valuable to future users no matter what the result, so I don't see the point of trying to shut it down by saying "just do what we already know is safe"
All people are trying to do is stifle the "it's fine, do it" sentiment. Most people are using Mac Pros for tasks that are important enough that they don't need downtime. It would be one thing if the target audience was overclocking gamers. But when your livelihood is on the line you should be VERY aware when you're treading into a gray area, even if it's probably ok.
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Old Dec 14, 2012, 07:43 PM   #18
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In order to get a solid answer we should look for a way to measure the resistance of the traces on the logic board.
If it's less than 50 Milliohms they should not have a problems handling 10 amps... As long as the PSU is not limiting of course.
Good point. Someone pointed out in the other thread that the logic board delivers 20amps from the PSU to the daughter board, so it's as easy as using larger traces to deliver the same amount of power to the PCIe aux power plugs. However, the plugs themselves are only rated at 108w and I don't think anyone has ever found solid info on the traces themselves. But, like I stated in that thread, it would probably be safe to assume that the bottleneck in that line would be the PCIe aux plugs rather than the traces. If they're rated at 108w, it's likely that the traces are rated higher.
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Old Dec 14, 2012, 07:53 PM   #19
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Originally Posted by brentsg View Post
All people are trying to do is stifle the "it's fine, do it" sentiment. Most people are using Mac Pros for tasks that are important enough that they don't need downtime. It would be one thing if the target audience was overclocking gamers. But when your livelihood is on the line you should be VERY aware when you're treading into a gray area, even if it's probably ok.
Fair enough. Forgive me for encouraging a dialogue that goes beyond the "avoid it at all costs" sentiment, but progress can only be made through questioning the norm.
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Old Dec 15, 2012, 06:25 AM   #20
macz1
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Another idea for 8+6pin GPUs:

6pin of the GPU -> LB AUX plug 1
8pin of the GPU -> LB AUX plug 2 plus power cable from the optical drive bay

The optical drive(s) is probably using just a fraction of what its power connector can deliver. It shouldn't be a problem to use it to help powering the GPU...
This will involve some splitting&soldering, however.
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Old Dec 15, 2012, 07:36 AM   #21
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The morons who have perpetuated this "Free Money from the Government" thought process have overlooked a few pertinent details.

Whilst claiming that one of the 6 pins can easily provide 150W, they forget that when the guy in Germany counted on BOTH 6 pins to provide power at 8 pin levels, he ruined his logic board.

They also forget the simple mechanics of how these adapters work. Most take power from 1 pin and provide it to 2 or 3. So, one pin gets asked to provide current of 3. 1 trace on logic board provides power of 3. If someone would like to argus this, I have 4 different 6 to 8s I can use as examples, they all will fry your logicboard over time. The extra current goes to 1 pin, which means 1 trace.

And here is the one that various Einsteins have somehow overlooked.....read about houlihan, or whatever his name was from Germany. When his Mac crapped out, it wasn't JUST the GPU that acted up, it was also his raid card that quit.

So, it wasn't the traces that ran to the 6 pin power plugs. It was the traces that provided 12V current to PCIE slots. As in multiple slots got at least 1 dead trace.

When 6 pins yanked too much current from PSU, power got sucked through PCIE traces which burned, taking out power to multiple slots.

He was running 2 @ 8 pins via 6 pins, what you are all saying should be just fine.

As to the assertion that I am saying this because I sell cards which use dual 6 pins. HORSE SXXT !!! Why would I choose to sell "2nd Best Mac GPU" when I could sell "Best"?

All of my GTX580 ads contain verbiage about getting a 2nd PSU, killing sales. If I was an irresponsible bozo, I would say "Get a 580 with a 6 pin to 8 pin adapter, it'll be fine". Nobody buys our 580s because getting a 2nd PSU is a PITA. I wish I could be like reveler and say that there is limitless power, so keep adding adapters.

I can't say that, so our 480 and 580 sales are CRIPPLED because I can't responsibly say that this will always work. Believe me, I wish I could. Check the bare feats.com results, the 580s KILLED all the other GPUs. I wish I didn't have to give people good advice, but telling everyone that running a 580 via 6 to 8 is a good idea would be almost as irresponsible as telling them to get a 7970.

Use your heads, people. There is no free government money, there is no free lunch, and thinking that you can use adapters and magically DOUBLE the output of Mac logicboard traces is simply "magical thinking".

The guy KILLED his logic board. Because he didn't want to spend $40 for a PC PSU. Think about it.
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Old Dec 15, 2012, 07:51 AM   #22
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So, to round up the logical statements that don't err on the side of risking a burnt out Mac Pro mobo:

If you want the best AMD card for your Mac Pro use a 7870 or 7950 with 2 6-pin connectors, if you want the best Nvidia card use a GTX670 or GTX570 with 2 6-pin power connectors.

http://www.hardocp.com/article/2012/...o_card_review/ AMD 7870

http://www.hardocp.com/article/2012/...o_card_review/ AMD 7950

http://www.hardocp.com/article/2012/...o_card_review/ GTX670

http://www.hardocp.com/article/2011/...eo_card_review GTX570

If you are a rabid overclocking OS X gamer, build yourself a PC tower with the power support for a juicier card and Hackintosh it.

Either of the above will happen for me when I eventually migrate to Mountain Lion.

Last edited by gpzjock; Dec 15, 2012 at 08:08 AM.
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Old Dec 15, 2012, 08:27 AM   #23
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So, to round up the logical statements that don't err on the side of risking a burnt out Mac Pro mobo:

If you want the best AMD card for your Mac Pro use a 7870 or 7950 with 2 6-pin connectors, if you want the best Nvidia card use a GTX670 or GTX570 with 2 6-pin power connectors.

http://www.hardocp.com/article/2012/...o_card_review/ AMD 7870

http://www.hardocp.com/article/2012/...o_card_review/ AMD 7950

http://www.hardocp.com/article/2012/...o_card_review/ GTX670

http://www.hardocp.com/article/2011/...eo_card_review GTX570

If you are a rabid overclocking OS X gamer, build yourself a PC tower with the power support for a juicier card and Hackintosh it.

Either of the above will happen for me when I eventually migrate to Mountain Lion.
Or you can just hook up a 2nd PSU.

----------

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Originally Posted by macz1 View Post
Another idea for 8+6pin GPUs:

6pin of the GPU -> LB AUX plug 1
8pin of the GPU -> LB AUX plug 2 plus power cable from the optical drive bay

The optical drive(s) is probably using just a fraction of what its power connector can deliver. It shouldn't be a problem to use it to help powering the GPU...
This will involve some splitting&soldering, however.
You're forgetting that the SATA power connector in the optical bay is not rated for that kind of amperage.
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Old Dec 15, 2012, 09:05 AM   #24
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Or you can just hook up a 2nd PSU.
As MVC states the sales of his GTX580 cards are nerfed into the ground by the phuqery involved with an additional PSU. I really wouldn't bother considering his experience of trying to sell that concept.

Furthermore Anandtech's bench of 7970 vs 7950 shows a 85-95% performance yield from the lower wattage card. 10% more grunt for 100 more, an extra PSU and a Mac that looks like it needs life support.
http://www.anandtech.com/bench/Product/508?vs=550



"You're forgetting that the SATA power connector in the optical bay is not rated for that kind of amperage."

Agreed.

Last edited by gpzjock; Dec 15, 2012 at 09:17 AM.
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Old Dec 15, 2012, 10:09 AM   #25
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You're forgetting that the SATA power connector in the optical bay is not rated for that kind of amperage.
True, the SATA power connector is not equivalent to a full 6-pin PCIE connector, but it's at least rated for 5 Amps on the 12V rail.

In my opinion this should be enough to shift the operation of a 7970 in a Mac Pro from "out of spec: works, but who knows how long" to "does slightly exceed the combined power spec when pushed to the extreme (if at all)"
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