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.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 dont required pin numb er two to have power, but it also does not prohibit it either.
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. Im running a NVIDIA STRIX 980 Ti OC with two 8 pin plugs (150w 150w 75w 375w). 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. 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 Apples are notoriously bad.) I dont 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 dont 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. ![]() 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. Pcie Video Cards Pro Full PCIe 2It 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. Radeon HD 7970 it is a hardware issue. 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. 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.
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