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MacPro Powering GTX 670 and hd5770 simultaneously?

Last response: in Graphics & Displays
November 25, 2012 12:55:53 PM

So I've come to this dilema where I've bought a Galaxy GTX 670 4gb GC for my mac (temporarily until I can get more money to build a pc) but I am uncertain if the power outputs on the mac are enough to run the GTX 670 and a HD5770 simultaneously. By simultaneously I mean just having both of them in the system at the same time but only using one. I use the 5770 for my regular OSX parathion, and the GTX 670 for my bootcamp to play demanding games; mainly skyrim with 4k textures and 40 plus mods, which is why I bought the 4gb version.
The 5770 requires one mini pcie 6 pin to pcie 6pin cable
but the gtx 670 requires one mini pcie 6 pin to 6 pin and a mini pcie 6 pin to pcie 8 pin cable
There are only 2 mini pcie 6 pin outputs so I figured I'd but a y splitter.
MacPro 2008 (3,1) 2 x 2.8ghz Quad-core intel Xeon
OSX 10.7.5 lion (I will be upgrading to mountain lion, 10.8.2, when I get the 670)
6GB DDR2 800mhz FB-DIMM
128GB Samsung 830 SSD
1tb WD Black caviar drive for storage
500GB WD green drive for windows
160GB time machine backup for the SSD

Apple AMD HD5770 (108 watts)
Galaxy GTX 670 4GB GC (it's factory overclocked to the clocks of a stock gtx 680) (The max wattage of a Evga gtx 670 2b supoerclocked is 170 watts)

Some specifics on the cable being used.
mini pcie 6 pin to 8 pin - 18awg rate at 110 watts
mini pcie 6 pin to 6 pin - 20awg rated at 78 watts
I will be replacing the mini 6pin to 6pin with a
mini pcie 6pin to y split 6 pin - 18 awg rated at 110 watts

so at idle the 5770 uses 18 watts
and the gtx 670 uses 18 watts

power usage of gtx 670 over clocked playing skyrim

i don't know if i'm reading it wrong but the total wattage with the gtx 670 is 388w, -160 of the computer = 228 watts which seems to
be over the 178 watts that the gtx 670's max is at, but i may not be accounting for other hardware. 228 + 18 watts for the idle 5770 =246w which is still under the 300 watts
but doing the math and having both pcie powering 85 watts and the 50 watts from the slot i would be left with 8 watts that can't be supplied. this is suggesting that the 50 watts from the pcie slot for the 5770 will power that.

I got mixed information about the power supply of the macpro 2008, it was either 960 watts or 1400 watts.
the apple website says that the pcie slots support up to 300 w for graphic cards. That's enough for the two graphics cards total max wattage (278) but I was wondering how I would deliver that. I was told by a guy that makes pcie cable for macs that the slots supply 50 watts of power and the pcie plugs ecch supply around 75-85 watts. but that they maybe able to supply 100w temporarily.

i've started babbling but, if anyone has had a similar setup or anyone that can point out any wrong things i'm doing or could do please let me know. Some of this information could be wrong, i'm only a semi-experienced user.

a b U Graphics card
November 25, 2012 1:35:18 PM

Hate to tell you this but a PC video card will likely not work in a Mac. The Mac video cards have a specific firmware that is only supported on Macs.

The only 2 ways around this are flashing the firmware on the card with one supported by Apple or build a hackintosh.


It looks like as long as you are running 10.8.2 it should work. You will not be able to see the boot screen and you will only be able to use the 670 by itself unless you have a low end card that does not need external power. They also recommend a reference clocked video card as an overclocked card can surpass the available power that comes from the 2 6 pin connectors (an 8 pin adapter will work also but have been known to have some issues with factory overclocked cards). However you will need a special driver if you are running a card over 2gb.

All information can be found here -->
November 25, 2012 1:40:28 PM

ish416 said:
Hate to tell you this but a PC video card will likely not work in a Mac. The Mac video cards have a specific firmware that is only supported on Macs.

The only 2 ways around this are flashing the firmware on the card with one supported by Apple or build a hackintosh.

actually os x 10.8.2 supports nvidia cards along with cuda support and the 4gb it just deosn't show the boot screen.
and I plan on using the gtx 670 in windows under bootcamp which supports mostly any graphics card.
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February 19, 2013 3:20:49 PM

Hi mate ! My case is almost the same and I was looking for such one, finally found it :)  Have you solve it? Is it possible to run theese two cards (I want to buy 660) together in MacPro ? Can Radeon be set to use only bootscreen and the second one to run system from loging? Please let me know :)  My mail is Thanks in advance :) 
March 10, 2013 8:32:40 PM

Yesterday got a EVGA GTX670. It seems to work fine after the CUDA and Drivers update on 10.8.2. The only problem is that this card has no Mini Display ports so I am waiting for this adapter to be able to use my Cinema Display and a plasma (DVI):

I also have the 5770, I was thinking on using both, so I can have my login window back. Currently if I use the 670 there is no login window, I have to auto login.

What would be the result of using both? Do I get better performance using both?

I mainly use this system to run Autodesk Smoke.
March 14, 2013 8:39:56 PM

I just updated to 10.8.3 and I have the Login Window and some issues with Smoke are now OK.