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Old Dec 19, 2012, 03:33 PM   #1
PoloSwelsen
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Mac Pro GTX 660Ti x 2

Hey Guys,

I recently bought a GTX 660Ti Graphics card for in my 8-core Mac Pro 2010. It works fantastic!! however i was wondering if there is a possibility to run two of those in one Mac Pro without using a external PSU.

I know you only have two 6pin connecters in the Mac Pro, but is there a way you can split each connector so that you will have 4 6pin connectors instead of two?
that way it would be possible to have two GTX 660Ti's in a single Mac Pro, right?

and what about the PSU, will it be enough? i've read somewhere that the Mac Pro's PSU is about 1000 - 1300W. But i'm not sure though.

Please let me know because i would lóve to have 2 of these amazing graphics cards!
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Old Dec 19, 2012, 04:21 PM   #2
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I wouldn't recommend it. IIRC the cables wouldn't be able to supply enough power. You'd be better off powering the other card with an external PSU.
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Old Dec 19, 2012, 04:24 PM   #3
PoloSwelsen
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So what is the maximum power that the Mac Pro can deliver to video cards? The 660Ti uses 150-200 max! Do you really think that 400W is too much?
I really don't want to use an external PSU. (Looks really ugly)
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Old Dec 19, 2012, 04:31 PM   #4
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Not suggested at all, but you could go just one GTX 680. 300W is the max suggested for total power draw on all PCIe lanes together including the 2 x 6pin power cables.
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Old Dec 19, 2012, 04:33 PM   #5
PoloSwelsen
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I've read that the GTX 680 wouldn't fit in a Mac Pro and I believe it doesn't come with 6 pins but with 8 pin connectors ):
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Old Dec 19, 2012, 04:53 PM   #6
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Originally Posted by PoloSwelsen View Post
I've read that the GTX 680 wouldn't fit in a Mac Pro and I believe it doesn't come with 6 pins but with 8 pin connectors ):
Only fancy-pants models have the 8-pin connectors. Normal GTX 680 models have two 6-pins.
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Old Dec 19, 2012, 05:13 PM   #7
PoloSwelsen
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I have an EVGA GTX660Ti and I found a power consumption of a super clocked GTX 660 Ti by MSI which says the maximum power use of this card is 146W... But doesn't a super clocked card consume more power?
Still two sc cards would not consume 300 W (146x2=192).
Let's say power usage isn't the issue, CAN I split the 2 x 6 pin to 4 x 6 pin or would I overheat the motherboard with doing that or would it be fine?

Ps is there a simple way I can stress out my GPU and measure the power usage?
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Old Dec 19, 2012, 05:27 PM   #8
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Originally Posted by PoloSwelsen View Post
I have an EVGA GTX660Ti and I found a power consumption of a super clocked GTX 660 Ti by MSI which says the maximum power use of this card is 146W... But doesn't a super clocked card consume more power?
Still two sc cards would not consume 300 W (146x2=192).
Let's say power usage isn't the issue, CAN I split the 2 x 6 pin to 4 x 6 pin or would I overheat the motherboard with doing that or would it be fine?

Ps is there a simple way I can stress out my GPU and measure the power usage?
Here you go: http://www.amazon.com/450W-Graphics-.../dp/B001AO4O98

It's internal so you don't have a box outside the tower. If you decide to use splitters it might overload the traces on the back pane. It may not. If you decide to split the power could you please let us know the results?
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Originally Posted by wildgiles View Post
Not suggested at all, but you could go just one GTX 680. 300W is the max suggested for total power draw on all PCIe lanes together including the 2 x 6pin power cables.
That 300W figure is excluding the two 6 pin cables from the back pane. It's 75W per PCIe slot and then it's 150W combined from the 2x 6 pin.
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Old Dec 19, 2012, 05:27 PM   #9
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Originally Posted by PoloSwelsen View Post
Let's say power usage isn't the issue, CAN I split the 2 x 6 pin to 4 x 6 pin or would I overheat the motherboard with doing that or would it be fine?
That's a really bad idea. Nobody knows how much power these will be pulling from the aux power connectors.

You know OS X doesn't support SLI, right?
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Old Dec 19, 2012, 05:44 PM   #10
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I am not putting an external PSU in my Pro, thanks for the tip though. That way it doesn't look that bad. Smart thinking.

Yes I know OSX doesn't support SLI. I think I will have to do it with this 660ti then. It isn't a bad card at all! I was just wondering. It is far better than the original 5770. Thanks for all your replies and great help!

I love to use adobe after effects and could use a little more cuda cores, so that's the reason I was wondering about a second card for the ones who like to know ;-)

----------

Theoretically, asuming one card uses 146W max. There wouldn't be a problem since each card will get 75W from the PCIe slot and half of the 75W from each 6pin adapter (2x37,5 = 75). So in total they will receive 150W when needed.
So you will stay beneath the 300W, and you'll not stress out the 6pin adapters...
Where is the problem then?
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Old Dec 19, 2012, 05:51 PM   #11
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Originally Posted by PoloSwelsen View Post
I am not putting an external PSU in my Pro, thanks for the tip though. That way it doesn't look that bad. Smart thinking.

Yes I know OSX doesn't support SLI. I think I will have to do it with this 660ti then. It isn't a bad card at all! I was just wondering. It is far better than the original 5770. Thanks for all your replies and great help!

I love to use adobe after effects and could use a little more cuda cores, so that's the reason I was wondering about a second card for the ones who like to know ;-)

----------

Theoretically, asuming one card uses 146W max. There wouldn't be a problem since each card will get 75W from the PCIe slot and half of the 75W from each 6pin adapter (2x37,5 = 75). So in total they will receive 150W when needed.
So you will stay beneath the 300W, and you'll not stress out the 6pin adapters...
Where is the problem then?
The problem arises with distribution, Will the card pull a clean 75W from the PCIe slot or will it pull less and the remainder from 1x 6 pin split in two? I would 'guess' it's 75W from the slot first and foremost but I couldn't say for sure. If it were me I'd go for the 2x 660ti as the power draw matches up within acceptable levels.
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Old Dec 19, 2012, 05:54 PM   #12
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And what if it reaches above the 75W per lane or 6pin adapter. Would that harm the computer? Or Would it just crash and turn off.
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Old Dec 19, 2012, 05:58 PM   #13
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And what if it reaches above the 75W per lane or 6pin adapter. Would that harm the computer? Or Would it just crash and turn off.
Nothing is known, some will tell you that it damages components, others will say the PSU will 'trip'. Theoretically it's possible, the PSU provides enough power but the channels that take the power to those 2x 6 pin connectors called 'traces' are not rated. As in nobody, at least here, knows how much extra drain they can handle. They may be 'thick' enough to handle twice the 75W, they might not be. If they can't handle the extra they could fry, melt, fizzle.

It's really an area of unknown and something many of us are looking into with interest. The only option is to pioneer and inform or go with a second PSU.
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Old Dec 19, 2012, 06:00 PM   #14
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Well than maybe i will do Some research on the max power usage a 6pin can handle and how much the card really uses, because I don't wanna melt my Pro actually ;-)
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Old Dec 19, 2012, 06:02 PM   #15
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Originally Posted by PoloSwelsen View Post
Well than maybe i will do Some research on the max power usage a 6pin can handle and how much the card really uses, because I don't wanna melt my Pro actually ;-)
If you want to be safe (Best to be) then go with a second PSU if using more power than a 5870. It really isn't worth the guess if you want a stable, worry free machine. Best of luck.
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Old Dec 19, 2012, 06:21 PM   #16
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Originally Posted by PoloSwelsen View Post
There wouldn't be a problem since each card will get 75W from the PCIe slot and half of the 75W from each 6pin adapter (2x37,5 = 75).
How do you know that is the distribution? What if it pulls the 150W evenly over all three? 50+50+50. Then the second card does the same, and you are pulling 100W each over the aux connectors spec'd to 75W each.
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Old Dec 23, 2012, 01:26 PM   #17
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How do you know that is the distribution? What if it pulls the 150W evenly over all three? 50+50+50. Then the second card does the same, and you are pulling 100W each over the aux connectors spec'd to 75W each.

That's true. I will do some more research (i recently found out that the card will reach 130-140W MAX). As soon as i know more, i will let you guys know.
Thanks for all the help!
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Old Dec 23, 2012, 10:20 PM   #18
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If this card only pulls ~140 watts, why does it need 2 6 pin plugs .... Wouldn't it get its power needs from just the pci slot and 1 6 pin cable?
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Old Dec 24, 2012, 12:00 AM   #19
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I have 2 gtx 660's in my Mac Pro and although they only use 1 6-pin each, the power usage is only a bit less than the 660 ti. I reckon the power will be fine, you just need to figure out how to plug them in due to lack of cables/ports.
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Old Jan 1, 2014, 04:40 AM   #20
Kennethlyon88
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To everyone,
Tbone mentioned that he is running two GTX 660's in his Mac Pro. If so, do I have to remove the bridge connector when using OS X? I play mostly games on my Win7 64-bit partition. I get good frame rates running medium settings on my HD5870 running Battlefield 4. However I have to play lowest settings for Metro Last Light.

I want to upgrade to the EVGA GTX 660 SuperClocked because it seems like a nice card and I can achieve over 32 fps on 1080p with high settings for both titles in one card. Furthermore, since it uses only one 6-pin connector... Why not get two and SLI both. I was told neither Xfire and SLI work on OSX, but it does on Windows through bootcamp.

Should I just save up and get the EVGA GTX 680 MAC Edition? Or I could use both 660's and save myself $200+?
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Old Jan 1, 2014, 04:45 AM   #21
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Hey, i just recently upgraded my Mac Pro from a 660Ti to a 680 4GB version with 2x6-pin. NOT The Mac edition. And it works delightful! So I think that that will be your best option since SLI does not work as good as it should. Many games and other software does not support SLI / crossfire.
Consider having 1 ultimate card instead of 2 other cards
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Old Jan 1, 2014, 12:53 PM   #22
Kennethlyon88
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PoloSwelsen
That what I was ultimately thinking about it. However, if I go with the GTX 680 Non-MAC, Did you get a booting screen?
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Old Jan 1, 2014, 12:59 PM   #23
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No you won't have a bootscreen. But why would that be a problem?
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Old Jan 1, 2014, 02:41 PM   #24
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I need it to be able to choose Mac or Windows through bootcamp. Otherwise, I have to flash the card to be able to have a boot screen.
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Old Jan 1, 2014, 03:19 PM   #25
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I need it to be able to choose Mac or Windows through bootcamp. Otherwise, I have to flash the card to be able to have a boot screen.
Use BootChamp(direct download). It's an OSX app to switch to boot camp partition. It puts an icon in your menubar.
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