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Question: MAC PRO 4,1 and 5,1 PCIe AUX Power

Mac Pro 4,1 & 5,1 have plenty of PCIe AUX power, unless you need more than 300 watts for your GPU(s). Remember you get 75 watts from the PCIe slot for GPU cards. Each PCIe AUX 6 pin connector in the Mac Pro towers delivers 150 watts. Yes all three power pins in both of the PCIe AUX plugs are connected. The PCIe specifications don't required pin numb
er two to have power, but it also does not prohibit it either. In the MAC Pro 4,1 / 5,1 it is connected. To be clear, this delivers the same power as a 8 pin connector without the extra sense and grounding pin on the 8 pin plug. Just buy the correct 6 to 8 Pin PCIe AUX cables and you ar
e all set. I'm running a NVIDIA STRIX 980 Ti OC with two 8 pin plugs (150w + 150w + 75w = 375w). The Mac Pro 900+ watt power supply can handle it. I also have t
wo 130 watt x5690s. No issues during stress testing.
Make an intelligent choice. If you use something more, it should wear out sooner. Some of these machines are 7 years old and taxing a 7 year old power supply can cause it to reset or become inoperative.
In researching this topic, GPU cards can have the 8-pin connector, but this has not been standardized yet, these cards do not carry the official PCI Express logo. This configuration will likely be standardized by PCI-SIG with the PCI Express 4.0 standard. But the design is there for these power hungry GPUs. Here is some great information about computer power and how much you can use.

Posted on Mar 7, 2017 8:34 AM

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Mar 23, 2017 5:08 AM in response to dustswap In response to dustswap

Yes in theory the GTX-970 should be faster, this is certainly the case in Windows. I found this comparison http://gpu.userbenchmark.com/Compare/Nvidia-Quadro-4000-vs-Nvidia-GTX-970/m7693v s2577 for Windows.

However doing the same search I found lots of reports of awful performance of the GTX-970 in a Mac Pro. 😟 However to be somewhat fair many of these reports are comparing the 970 in a Mac vs Windows and not compared to other Mac cards. (Mac video drivers - especially Apple's are notoriously bad.)

I don't have either a Quadra 4000 or GTX-970 myself so cannot speak from personal experience, I had thought most people went straight for the GTX-980 or 980Ti as the current top Mac compatible models. (I don't have those either.)

Since the GTX-970 has never officially shipped in a Mac edition you are obviously using a PC edition of this card. Whilst having Mac firmware flashed on to it should make absolutely no difference to performance it maybe a PCIe 2.0 issue. Can you open 'About this Mac', then click on 'System Report…' and then click on 'PCIe' and look at the information for the GTX-970. You need to look for link speed and the number of lanes being used. If you can let us know and ideally post a picture of this. It is the Link Speed i.e. GT/s that is most relevant.

It could be that despite the fact the GTX-970 is a PCIe 3.0 card and should work at full PCIe 2.0 speed in your Mac it might only be working at PCIe 1.0 speed. MacVidCards who 'flash' PC Edition cards to Mac firmware also fix these sorts of issue as well which sometimes means making a small hardware modification to the card. As an example I did this myself to one of my Mac video cards which was formerly a PC Edition. I think if I remember correctly fixing the PCIe speed issue on Nvidia cards is a firmware related issue, and for some AMD cards e.g. the Radeon HD 7970 it is a hardware issue.

Obviously if your GTX-970 is only operating at PCIe 1.0 or 1.1 speeds it will be severely handicapped.

Mar 23, 2017 5:08 AM

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Mar 7, 2017 9:27 AM in response to syops In response to syops

The 6pin PCIe aux-power connections like all 6pin aux-power connections i.e. including PCs only provide 75w each. Therefore both 6pin connections plus the PCIe slot itself only gives a maximum of 225w.

Your information must be out of date because many video cards do have 8pin power connections and do so because they require more power than a 6pin power connection can provide.

If you try drawing 150w i.e. what an 8pin connection uses via a 6pin cable - presumably using an adapter then you run the risk of melting the very thin circuit traces on the Mac Pro logic board. At best you will trigger the Mac Pro in to shutting down to prevent such an overload.

So while a Mac Pro has a 980w power supply and from that perspective might be considered to be more than powerful enough for a video card needing 300w the connections in a Mac Pro simply do not support this. If you need to drive a video card needing that level of power you must use a second power supply with additional 8pin connections to provide the required power. Such a second power supply could be external to the Mac or there are ways to fit it inside the Mac in the lower normally empty optical drive bay.

Note: In various Mac forums there have been plenty of reports of people trying to use a video card that needs more than the 225w officially possible with 6pin cables and this then as mentioned results in the Mac Pro shutting down. If you need say 250w as this is only slightly above the official limit you can probably get away with it, if you need 300w or more then you risk damage or a shutdown.

See this article and especially the two links for whether you do need a second power supply and how to fit one internally in the Mac Pro. http://www.macvidcards.com/do-i-need-an-additional-power-supply.html

Mar 7, 2017 9:27 AM

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Mar 7, 2017 10:30 PM in response to John Lockwood In response to John Lockwood

Here is a ASUS STRIX GTX 980 Ti OC running 3DMARK with a 30% overclock. The card needs two 8 pin PCIe AUX and is provided from the Mac Pro 6 pin PCIe AUX motherboard headers. The Mac Pro 6 pin PCIe AUX headers are connected with all three power pins, the same number of power pins on the 8 pin PCIe AUX.

You just need the correct mini 6 to 8 pin PCIe AUX cables.


User uploaded file

Here is a great source about PCIe AUX power.


Mar 7, 2017 10:30 PM

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Mar 8, 2017 5:08 AM in response to syops In response to syops

I do not see any references via the links you provide which substantiates the fact that Apple provide three power pins on their 6-pin connections. All the links you provide discuss things from a PC perspective. What I can agree with is that hypothetically a 6-pin connector with three power pins might do what you claim.

The issue remains that unlike the majority of PCs the Mac Pro routes these power pins via traces on the main Mac Pro logic board. It is not thick wires routed directly to the PSU. As a result these very thin logic board traces inherently have less capacity than thick separate wires. If these thin traces are overloaded they would melt destroying the entire logic board.

Without firm technical evidence to the contrary even if one believes that all three power pins are connected two or more could be using the same single trace meaning you would be even more likely to over stress that thin trace.

The fact you can fit a video card that comes with an 8-pin power socket is not proof the Mac even with a suitable cable will deliver the right amount. Most of the time most users of video cards do not run them heavily and the card therefore will not need to draw its maximum potential load. I my self have fitted a Radeon HD 7970 which has a 6-pin plus an 8-pin connector and it worked but I was no where near stressing it as I was not doing rendering or games.

You mention special cables for the Mac Pro but do not provide any evidence they exist. A link would be much appreciated. Even the 'standard' Mac Pro aux-power cables are 'special' since they go from a unique Apple mini PCIe connector to a standard 'large' GPU 6-pin connector. The fact the 'normal' Apple aux-power leads may have all six wires present is not itself evidence the logic board provides also six separate traces.

You are literally the only person I have so far seen that claims the Mac can safely do 150w via the Mac Pro's 6-pin aux-power connectors. All the other reports I have seen including the link I provided from a very reputable source state you cannot/should not do this.

Mar 8, 2017 5:08 AM

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Mar 8, 2017 6:54 AM in response to John Lockwood In response to John Lockwood

The fluke test. So I will show you that pin two is connected in the following pictures. The references above indicate that pin 2 may or may not be connected on the 6 pin PCIe AUX. Only pins 1 and 3 are required by specification for the 6 pin. 8 pin PCIe AUX power connectors were specified in 2007 for PCI express 2.0. That spec requires pin 2 to be connected and adds an additional sense and ground to the plug. The MAC PRO is PCI Express 2 , and I think Apple designed and biult it to those period specifications. Here are the pin outs for the cables.

User uploaded file

Displayed in the above pin out the only pins that provided power are 1,2 and 3 on both the 6 and 8 pin connection. Again the 6 pin official specification is to have pin 2 not connected. But on the MAC PRO 4,1 and 5,1 pin 2 is connected. First look at this typical 6 to 8 pin PCIe AUX cable.

User uploaded file

This is a very typical PCIe cable configuration. The PSU only needs a 6 pin plug and if your GPU needs 8 pins the addition pin are just jumpered to provide the ground and sense connections. Some have said the cables or traces will overload, but that is not the case. The cabling is well over built. In the previous reference and this one here the minimum cabling for the speciffcation is 18 gauge. 18 guage can handle a maximum current load of 16 amps. Molex 8981 connectors are ratted for 8 amps with 18 AWG.

Cable reference and prior reference



Here are the meter tests showing pin 1,2 and 3 connected in the MAC PRO 4,1 and 5,1.

User uploaded file

User uploaded file

User uploaded file

It would be really great if an Apple engineer would pull the MAC PRO 4,1 and 5,1 design specifications. That will never happen.

As you can see all 3 pins are connected. The current load is controlled by the GPU. With both sense pins connected the GPU will pull up to 150 watts if the PSU will handle it. These machines are old now and the PSUs may not be up to specification or damaged. I think this is where you see some MAC PRO shut downs. Also overclocking. What happens when you push your overclock to far? The equipment becomes unstable and then what? Anything can happen. The GPU could just rest it self or the computer could just shutdown.

I have 2 MAC PRO 2009s with upgraded firmware to 5,1. Both have dual x5690 CPUs. The GPU is a ASUS STRIX GTX 980 Ti OC and requires two 8 pin PCIe AUX connections. Very stable machines under Sierra and windows boot camp. Even with the 30% GPU overclock I have no issues.

Mar 8, 2017 6:54 AM

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Mar 8, 2017 7:28 AM in response to syops In response to syops

Yes but pin 2 could be linked to pin 1 or 3 on the logic board and might not be a separate wire just as per your picture one plug is linking pins 4 and 8 to other pins. It could be either end of the logic board that they might be joined or hopefully not joined at all.

The traces on the logic board would I believe be far lower capacity than normal e.g. molex type wires.

It maybe the 'apocryphal' stories about logic boards burning out relate to earlier Mac Pro models e.g. MacPro1,1 to 3,1 which had older versions of PCIe slots. There are however a lot more stories including for 4,1 and 5,1 models of Macs simply shutting down when overloaded but this might be simply the use of incorrect cables.

Have you established if the Apple provided mini PCI to PCI cables have all the pins wired? These are the cables most people will be using. I suppose I will have to get my own multi-meter out. 😉

I do appreciate your posting this, it is useful information and means using a single high power card is more realistic whilst using two such cards definitely still needs a second PSU. (Someone else has today asked about using two R9 280x cards.)

Mar 8, 2017 7:28 AM

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Mar 17, 2017 7:09 PM in response to dustswap In response to dustswap

Looking up your cards power usage I think a standard 6 pin min to 8 pin plug will be just fine. Amazon.

NEW Mini 6-pin to 8-pin Pci-e Video Card Power Cable for Apple Mac Pro/g5 https://www.amazon.com/dp/B00PVJ2DNC/ref=cm_sw_r_sms_c_api_gHiZybH2BNF7P

Just read the other Mac Pro user reviews there. They are happy.

Mar 17, 2017 7:09 PM

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Mar 18, 2017 1:51 AM in response to syops In response to syops

Thanks for quick response! This is where i get lost. After reading all over the place about this subject.


"Also be aware that the 6pin mac connector is rated for 75watt max, and the 8pin is usually 150watt so if the card trys to draw 150 through it then there is a risk of damage to the mac's logic board."

2. Qutoe:

"Single 8pin equals dual 6pin, both are rated @ 150W."

And this is my problem which of the quotes is right( my card 225w) ?

1. mini 6pin to 8pin cabel = 75 w + PCIe 75= 150w ( missing 75w ?!)

2. mini 6pin(75) + mini 6pin(75)PCIe adapter to a 8pin + PCIe 75w= 225w.

What is true? I just want to know if i need a single mini 6pin cabel to 8pin as you suggested , or will i need a dual mini 6pin to 8pin adapter? I know nothing about electricty I'm just a keyboard warrior trying to find the right solution:)

Mar 18, 2017 1:51 AM

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Mar 18, 2017 8:02 AM in response to dustswap In response to dustswap

You are correct there are two ways to install this card. Using the Y adapter is a dual mini 6 pin to 8 pin PICe AUX cable. That will bridge the power from both mini 6 pin headers in the Mac Pro and power your card. Those cables seem to be harder to find, but I did find one for 15 to 20 dollars.

The other way is to use a mini 6 pin to 8 pin PCIe Aux cable and seem to be all over amazon. But you need to be sure your system and cable has the connected power on pin 2. If pin 2 is not connected then you will probable have the Mac Pro system thermal protection circuit shut the system down. I am looking into the specifics of this protection circuit.

Digging deeper. The Mac Pro 4,1 and 5,1 have a big power supply with a single 12 volt rail. Load balancing power from the power supply is not an issue because of this single rail design. I have tracked one of my Mac Pros hogging 671 watts, total system power, running 3DMARK benchmarks on an ASUS STRIX 980 Ti OC. That card has 2 - 8 pin PCIe AUX plugs and is setup for a total 375 watts. I power the 980 from the 6 pin headers on the Mac Pro motherboard. Works great.

Looking at the ASUS GTX 970 OC 4GB.

Tweak Town has a nice review and shows the card well below the 200 watt range.

http://www.tweaktown.com/reviews/6789/asus-geforce-gtx-970-4gb-strix-oc-video-ca rd-review/index16.html

Tech|Inferno... they really go at it with each other... but again showing the 970 < 200 watts.

https://www.techinferno.com/index.php?/forums/topic/7881-gtx970-power-consumptio n-discussion/

Even my 980 Ti OC probably only uses around 300 watts.

Point is the Mac Pro PSU can handle both of these cards.

Your question about the magical 75 watts...??? where does it come from and how could that work?? right?

We need to have a look at the pin outs of both 6 and 8 pin PCIe AUX connectors.

User uploaded file

We will be focused on the left side of the diagram. What is important to notice is there are only 3 pins that can provide power on either the 6 or 8 pin PCIe AUX connectors / plugs. Note pin 2 on the 6 pin plug is not required to be connected. On the Mac Pro 4,1 / 5,1 it is. See picture.

User uploaded file

And that is my 6 to 8 pin PCIe cable.

Differences in 6 vs 8 pin PCIe AUX plugs.

They are the same if pin 2 is connected, the 8 pin adds two connections ( ground and sense ). The additional sense connection is what tells your GPU card it can pull power the higher power load. If pin 2 is not connected and you hack your card by shorting the second sense connection, this will overload the connections at pins 1 and 3. Don't worry the 18 gauge cables are ratted for way more amps. So no fire, but not good. Actually BAD. Don't do it. Where the issue occurs is possible in a thermal protection circuit on the Mac Pro mother board. ( No documentation on this protection circuit yet. But it sounds good. ) Power draw from the PSU is controlled by the GPU card. If the card has only one sense pin in the PCIe AUX connections, the GPU card will only draw the lower power load of a 2 power pin connection from the PCIe AUX cable. If you have both sense pins in the PCIe AUX connections, the GPU card will draw the higher power load of a 3 power pin connection from the PCIe AUX cable.

Wait if 6 and 8 are the same why have 8 pin specs?

The 6 pin PCIe AUX connection is only required to have 2 power pins. The 8 pin connector guarantees all three power pins are connected. The cables are made out of the same material. The connectors are made out of the same material. And again each header on the Mac Pro has all three power pins connected.

If I remember PCIe 2007 specs introduced the 8 pin PCIe AUX connection. The Mac Pro 4,1 / 5,1 Motherboard is a 2009 release. The 4,1 and 5,1 Mac Pro have the same motherboard. I believe the 2007 PCIe spec is why the 2009 Mac Pro has 6 pin PCIe AUX headers with all three power pins connected. In the following picture you can see the additional pins in an 8 pin connector have jumpers from the other pins ( ground and sense ). No additional power. I do feel it was Apples design intentions to provide full power from these headers.

User uploaded file

I am running a 30% overclock on my STRIX 980 Ti OC. It is stable using 2 - 6 to 8 PCIe AUX cables powered from the Mac Pro headers.

So where dose the extra power come from? Pin 2. Not all of the extra power. It should be shared from all three pins. Not all GPU cards are built the same. From my experience with ASUS, they design great power delivery systems. As I said earlier the GPU card controls power draw. If the engineering was poor, your might have an unbalanced draw from the three pins or from either of the headers if using a dual 8 pin GPU card. The Mac Pro PSU will not care because it is a single rail system. Because the power draw is controlled from the GPU card, it would be smart to have protection on the the PCIe AUX headers. The PSU has protection, but that is for total system power usage. These are both areas with limited documentation. Only user testing and experience has shown what can be done with the system. I am currently trying to setup a dialog with Apple Engineering. But it is not in their interest to support a discontinued platform that can perform better then the current Mac Pro 6,1 in the highest configuration. The 6,1 is a great machine, but has the GPU limitations. The old 4,1 and 5,1 Mac Pros are beasts. Currently I have two with CPU and the 980 Ti OC upgrades running in a production environment. STABLE.

I hope it helps.

Mar 18, 2017 8:02 AM

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Mar 18, 2017 10:48 AM in response to syops In response to syops


I bow my head in admiration ! Thanks for such a detailed answer, that really helps. I will buy the first cable you suggested and i will try to find the Y adapter as well. I work as a full time editor, and I'm running adobe creative suite . So the Gtx 970 is not ideal, I'm leaning more to the GTX 780 6GB with more Cuda cores (2304),at least on papper that sounds like a more powerful card to use. So i need to a few more cables to accommodate the future investment of GTX 780. Again thanks a lot for your help! Out of curiosity , what type of production do you do?

Mar 18, 2017 10:48 AM

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Mar 18, 2017 4:33 PM in response to syops In response to syops

Looks nice! i will upgrade later on. Now i have to test the GTX 970 first , but i will have to wait for cables for a few weeks. Unfortunately these cables doesn't exist in my country. The amazon link won't ship here either. So the hunt goes on:)

Nice to here you are in the business aswell. I don't do 3d at all, that extra dimension is to mutch... PP, AE, IS,PS and mixing in AU is my everyday tools. But i have seen some amazing work with octane and C4d that our go to guy does. Again thanks for all the help! Time for some cable hunt !

Mar 18, 2017 4:33 PM

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Mar 22, 2017 1:31 PM in response to syops In response to syops

Hi again!

So i managed to find a 6 to 8 pin adapter. First test with the GTX 970 was disappointing. I rendered 4 layers(3 of the scaled) of 4k , totalt length of 1min to h264 4k (premiere pro CC 2017). With my old Quadro 4000 card using cuda = 4min 52 s . And with GTX 970 with cuda enabled = 6min 40s ?! Something must be wrong? Is the GTX 970 running in slower speed ? I thought the GTX would smoke the Quadro with less cuda cores and VRam.

Mac Pro 5.1 CPU :3.33 GHz 6-core Intel Xeon

OSX macOS Sierrra 10.12.3 : Samsung 850 500gb EVO

Video/Projekt files/Cache/Scratch: HyperX Predator 480GB PCIe HHHL SSD

GPU: GTX 970 OC 4GB with Nvidia Webdrivers

Mar 22, 2017 1:31 PM

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Question: MAC PRO 4,1 and 5,1 PCIe AUX Power