Power over PCIe x16 (x2 bandwidth)

[Bloste]

So, a full x16 PCIe slot can deliver 75w to a GPU. But a x16 phisical slot limited to x2 bandwidth by the motherboard? Can it deliver those 75w, or is it limited to the 10w of the x2 bus?

Just thinking of using an old 1030GT as a PhysX card...

 

[Carillon]

the slot power is the same for 1x to 16x, what changes is the number of data lanes

 

[londiste]

the slot power is the same for 1x to 16x, what changes is the number of data lanes

That is not strictly true if we talk about PCIe spec. Manufacturers can and often do provide or consume (because draw is usually determined by the card) more but spec does define different power levels for add-in cards.

For x1 card its 10W, 4x or 8x its 25W and for x16 GPUs its 25W at boot and 75W later.
There are more ifs and buts there - spec allows some x1 cards to draw more - IIRC based on length and intended for server cards. And the limit is for 3.3V and 12V combined. Plus, technically low-profile cards are supposed to have lower power, including x16 remaining at 25W.

Edit:
For practical purposes you should be fine for the full 75W.

 

[Bill_Bright]

"Can" deliver 75W does not mean the slot "will" deliver 75W. It just means the motherboard is capable (by ATX Form Factor requirements) of delivering "up to" 75W, if the card demands it and if the card maker designs the card to use that full amount.

The intent is, for power hungry cards to have multiple sources for power thus ensuring no single source (PSU wire, for example) is overloaded. This distribution of power is what allows extremely power hungry cards to be supported even though no single circuit has the capacity.

Note that, by design, a power hungry card may only demand 40W through the slot, yet still demand 150W or more through the cable connections. And that's fine.

 

[Beertintedgoggles]

Shown in the two images attached, the power delivery is supposed to be the same regardless of the slot being physically x1 / x4 / x8 / x16. Whether or not the motherboard manufacturer followed this is best determined in the manual for that particular board. The extra pins in the larger connectors are all data.

 

[Bill_Bright]

Shown in the two images attached, the power delivery is supposed to be the same regardless of the slot being physically x1 / x4 / x8 / x16.

Ummm, where is it shown in those images the power delivery is supposed to be the same?

I see nothing about actual "Power" (as in watts and/or current) at all. What I see is the misleading labels of "Power 12V" and "Power 3.3V". Those are voltages. Voltage and power are not the same thing.

P = IE

That is, power (in watts) is the product of current (I) times voltage (E).

It would actually make no sense for the "power" to be the same simply because there could be totally different devices inserted in those slots. You might have a sound card in one slot and a WiFi adapter in another. For sure, the voltages on the respective pins will be the same. But the two cards would demand (and get) different amounts of power.

 

[_roman_]

Weird spec screenshot to not show the GND planes on teh peg connector.

 

[Bill_Bright]

Weird spec screenshot to not show the GND planes on teh peg connector.

Well, we don't see the whole image so we don't know the intent of the image, or what it was actually supposed to illustrate.

 

[Beertintedgoggles]

PCI Express - Wikipedia

en.wikipedia.org

You're going to have to scroll down and do the work yourself... Pins 1-11 Side A / Pins 1-11 Side B.

Edit: *Hint - It's under the Pinout section. If you're referring to delivery, then yeah it can depend on amount of Watts per slot size. I was getting hung up on pinout.

Edit #2: I keep submitting before I mean to, just below Pinout they lay out the Slot Power in the Power section. Would still suggest to look at manual to see if full power is available on slot in question.

 

[Bill_Bright]

Would still suggest to look at manual to see if full power is available on slot in question.

What manual? The ATX Form Factor standard requires all ATX compliant motherboard's ensure the slot is capable of providing 75W. So if not compliant, then it must a proprietary board and not standard.

It is up to the card maker to decide if they are going to demand that much, or not.

 

[Beertintedgoggles]

So, a full x16 PCIe slot can deliver 75w to a GPU. But a x16 phisical slot limited to x2 bandwidth by the motherboard? Can it deliver those 75w, or is it limited to the 10w of the x2 bus?

What manual? The ATX Form Factor standard requires all ATX compliant motherboard's ensure the slot is capable of providing 75W. So if not compliant, then it must a proprietary board and not standard.

It is up to the card maker to decide if they are going to demand that much, or not.

Not knowing if that's a physical x16 / electrical x2 (which would be strange in the first place... it's usually x16 physical / x4 electrical) or if it's a full x16 and is limited to x2 through bifurcation on the MB, the manual of the motherboard would spell it out.

 

[Bill_Bright]

Ah! Now I see what you were saying. Thanks for clarifying.

 

[Bloste]

Not knowing if that's a physical x16 / electrical x2 (which would be strange in the first place... it's usually x16 physical / x4 electrical) or if it's a full x16 and is limited to x2 through bifurcation on the MB, the manual of the motherboard would spell it out.

You're absolutely correct: It's a x16 physical, x4 electrical. I checked it in the manual before posting, and still managed to screw it up.