PCI-e 2.0 Wattage

[RayvinAzn]

Back before PCI-e 2.0 came out, I remember one of the more exciting bits about it (in my opinion) was a more flexible power provision for PCI-e 2.0 cards. I was under the impression that this would allow for more wattage to be provided through a PCI-e 2.0 slot, allowing higher wattage graphics cards to not use an external power connector, or at least not require dual or 8-pin connectors like some of our current (and upcoming) graphics hogs.

Taken from the PCI-SIG website:

Power limit redefinition ? to redefine slot power limit values to accommodate devices that consume higher power

I can't download the actual specifications of the interface, and to be quite honest I probably wouldn't understand most of it given my rather casual electronics background (10 months military O-level aircraft electronics schooling and 4 years swapping boxes and basic wire-chasing), but it seems to me like this is a feature of PCI-e 2.0 that hasn't been implemented yet for some reason. We weren't saturating the bandwidth of PCI-e 1.1 yet, the whole power issue was one of the big things I was looking forward to with PCI-e 2.0, but it seems forgotten.

What happened? Did I misread something (or many somethings)? Is this up to motherboard manufacturers/chipsets? Will this require a new motherboard connector with additional pins that nobody wants to adopt?

Moved to appropriate forum - Moderator Rubycon

 

[Extelleron]

The reason that PCI-e 2.0's additional power available through the slot hasn't been utilized is to maintain compatability with PCI-e 1.0/1.1 boards. I'm not sure if enabling the card to take 150W from PCI-e (which should be available w/ 2.0) kills all backwards compatability in itself or whether AMD/nVidia just don't want to worry about having to provide additional power connectors for those using PCI-e 1.1 and have the card require their use only when using the older interface.

 

[Modelworks]

I think the power part of pci-e 2.0 was one of those things that looked good on paper but in the end is not proving to be worth implementing for manufacturers. when you start trying to provide power in the 150W range on things like motherboards that already have problems with routing traces its just easier to provide the power by extra wiring external to the board.

 

[heymrdj]

Soon wires will run on top of the board instead of inside the board. Large 0/1 guage wires like we wire our car stereo amps with will come directly from the PSU and lock into the motherboard to run the 2 quad core Xeons we use as a Northbridge, the single QX9450 we use for a Southbridge, and 800W going to each gfx card. The future is perrty..

EDIT: Switched up some words there.

 

[Aluvus]

PCI-Express 1.x could supply 150 W per slot, PCI-Express 2.0 can supply 300 W per slot. More on PCI-Express 2.0.

Until PCI-Express 2.0 motherboards become more common, video card manufacturers have to assume that they are only guaranteed to be able to draw 150 W from the slot. So they still have to have external power connectors. If the designers are clever, it should still be possible to use most cards in a PCI-Express 2.0 motherboard that fully meets the power spec, without using the extra power connector.

 

[RayvinAzn]

150w per slot? I would have sworn it was only 75w per slot, 75w per 6-pin PEG connector, and 150w per 8-pin PEG connector. Thanks for the link Aluvus, that was a good read though.

 

[jonnyGURU]

Aluvus's is confused and that 10stripe website is completely wrong. It is only 75W through the slot. It looks like he's adding up slot power and PCIe aux power connector capabilities. You CAN NOT deliver > 75W through a PCIe 1.x slot and you CAN NOT deliver 300W through a 2.0 slot.

It's 75W through the slot, 75W per 6-pin PCIe and 150W through the 8-pin PCIe. Period.

Originally posted by: 10stripe website]
A single x16 slot may now be called on to deliver up to 300 W of power, up from 150 W. And the power supply connector used for graphics cards that need more power than the slot can deliver (sometimes called a PEG connector, for PCI-Express Graphics) has changed, from 6 pins to 8.

Ugh... Whoever wrote that, please fix. Using 10stripe's math, a graphics card could theoretically consume up to 600W!!!!!! Ummm.... no. The spec is called "300W" because there's a maximum theoretical consumption of up to 300W when the slot and both a 6-pin and 8-pin power connector are used. NOT 300W through the slot!!!

 

[Aluvus]

Originally posted by: RayvinAzn
150w per slot? I would have sworn it was only 75w per slot, 75w per 6-pin PEG connector, and 150w per 8-pin PEG connector. Thanks for the link Aluvus, that was a good read though.

Thank you for the correction.