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question about PCI Express

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  • Power Supplies
  • Motherboards
  • PCI Express
Last response: in Motherboards
June 15, 2014 12:55:58 AM

First question here;
pci express can provide maximum of 75 watts of power, right ? :??: 

if yes then how r9 295x2 is getting its 500 watts from ? :??: 

Thanks :D 

More about : question pci express

a b ) Power supply
a b V Motherboard
June 15, 2014 1:04:05 AM

Yes, PCI Express provides 75w

With most mid to high end GPU, you also plug in connectors from the Power Supply, to give more power.
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a b ) Power supply
a b V Motherboard
June 15, 2014 2:23:29 AM

For a number of years now the power supply has supported specific cabling for additional power to the graphics cards. There are 2 flavours of PCIe auxiliary cabling, 6 pin and 8 pin. I believe the 6 pin cable delivers an additional 125W while the slightly newer, and heavier, delivers 250W of power. Depending on the power requirements of the card it will have a combination of 6 and/or 8 pin sockets for that additional power. I'm pretty sure the GTX 690 had a triplet of 8 pin sockets while the mid range cards like the Radeon HD 7770 and GTX 660 has a single 6 pin socket. Everything else in-between has single or double sockets to suit its needs.
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June 15, 2014 3:15:29 AM

R9 295x2 requires 2 *8pin connectors which means 300 watts of power, add 75 watts from pci express ; still total of 375 watts far away from its rated consumption 500 watts :??: 
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Best solution

a b ) Power supply
a b V Motherboard
June 15, 2014 5:36:16 PM

The PCIe slot can provide 75W and a 8-Pin PCIe cable can provide upto 150W, I think these are only assumed values & a good quality power supply can provide higher power than these values as long as there is sufficient headroom.

According to the review of R9 295x2 on tomshardware(http://www.tomshardware.com/reviews/radeon-r9-295x2-rev...) , the average peak power consumption of R9 295x2 hovers around 450W. At load it only draws 28W from board itself which is far away from assumed value of 75W. So this basically means that the 2 × 8-Pin PCIe cable are providing 400+W of power to the GPU.(http://www.tomshardware.com/reviews/radeon-r9-295x2-rev...).

This is why only topmost quality power supplies are recommended to be used with Graphics card of high power consumption.
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