Recently got a motherboard with a pci-e connector on it and it makes me question GPU upgrades

[Factoring]

Hello.

So I recently got an MSI MAG-X870-TOMAHAWK-WIFI and it has a PCI-E connector on it. I'm thinking of upgrading to an 9070 XT, and I see some of them require 3 PCI-E cables plugged into them.

Doing the math, I require 2 cables for the CPU, 1 for the motherboard, and 3 for the video card. That's a total of 6 cables. But after browsing around for a little bit, all power supplies come with max 5 slots! That means I will have to use one cable for two connectors on the video card.

Will doing that hinder performance under max load? My guess is that it could prevent the video card from reaching 340W, but maybe the power delivery from the PCI-E slot saves the day? I really don't know. I don't have a power supply with a 16-pin 12VHPWR connector.

There are also other motherboards that also have a PCI-E connector on them. Do they run into the same issue then?

Thanks.

 

[nomdeplume]

Doing the math, I require 2 cables for the CPU, 1 for the motherboard, and 3 for the video card. That's a total of 6 cables. But after browsing around for a little bit, all power supplies come with max 5 slots! That means I will have to use one cable for two connectors on the video card.

Will doing that hinder performance under max load? My guess is that it could prevent the video card from reaching 340W, but maybe the power delivery from the PCI-E slot saves the day? I really don't know. I don't have a power supply with a 16-pin 12VHPWR connector.

Current PSU: 2x8pin mobo power + 3x8pin GPU.

Believe that extra connector is there for stability but doesn't need to be used. It probably exists to provide security of mind using a 16 pin.

 

[Marcus L]

Hello.

So I recently got an MSI MAG-X870-TOMAHAWK-WIFI and it has a PCI-E connector on it. I'm thinking of upgrading to an 9070 XT, and I see some of them require 3 PCI-E cables plugged into them.

Doing the math, I require 2 cables for the CPU, 1 for the motherboard, and 3 for the video card. That's a total of 6 cables. But after browsing around for a little bit, all power supplies come with max 5 slots! That means I will have to use one cable for two connectors on the video card.

Will doing that hinder performance under max load? My guess is that it could prevent the video card from reaching 340W, but maybe the power delivery from the PCI-E slot saves the day? I really don't know. I don't have a power supply with a 16-pin 12VHPWR connector.

There are also other motherboards that also have a PCI-E connector on them. Do they run into the same issue then?

Thanks.

CPU cables are 8pin and not the same as 6+2 PCIE connectors, neither will either of them interchange unless you force them and want to see some internal fireworks

 

[Factoring]

CPU cables are 8pin and not the same as 6+2 PCIE connectors, neither will either of them interchange unless you force them and want to see some internal fireworks

This is true, but they both go onto the same connectors on the power supplies. This one from ASUS only has 3 of them, for instance (they definitely expect you to be using the new connector instead).

 

[Arkz]

This is true, but they both go onto the same connectors on the power supplies. This one from ASUS only has 3 of them, for instance (they definitely expect you to be using the new connector instead).

View attachment 390479

It has a bunch of accessory connectors next to them that give you 4 pin molex connectors on the end. You could just use one of these

Also depending on your cpu you may only need one 8 pin cpu plug in.

 

[Hereticbar]

Doing the math, I require 2 cables for the CPU, 1 for the motherboard, and 3 for the video card. That's a total of 6 cables. But after browsing around for a little bit, all power supplies come with max 5 slots! That means I will have to use one cable for two connectors on the video card.

That's not true. It depends on the wattage of the power supply. I am pretty sure for most decent power supplies that are over 750w, it is not uncommon to see more than 5 CPU/PCIe 8 pin connectors on them. Although, on some power supplies a couple of the 8-pin connectors might be replaced with a 12VHPWR connector instead.

My Seasonic power supply from 2020, comes with 8 individual CPU/PCIe connectors. I remember wondering why it also came with 2 really nice drawstring bags, then I ended up with bags full of extra unused cables. So, that's what those bags are for.....

 

[eidairaman1]

That's not true. It depends on the wattage of the power supply. I am pretty sure for most decent power supplies that are over 750w, it is not uncommon to see more than 5 CPU/PCIe 8 pin connectors on them. Although, on some power supplies a couple of the 8-pin connectors might be replaced with a 12VHPWR connector instead.

My Seasonic power supply from 2020, comes with 8 individual CPU/PCIe connectors. I remember wondering why it also came with 2 really nice drawstring bags, then I ended up with bags full of extra unused cables. So, that's what those bags are for.....

Same in 2014, its nice to have them though

 

[Hyderz]

My Seasonic power supply from 2020, comes with 8 individual CPU/PCIe connectors. I remember wondering why it also came with 2 really nice drawstring bags, then I ended up with bags full of extra unused cables. So, that's what those bags are for.....

only thing i can think of is that sli was a thing back and the gpus needed those cables...

 

[eidairaman1]

The connector is supplemental, op should try it without using it and i only believe its for heavy overclocking anyway

 

[Fokker]

It depends on the specific PSU, but many come with more than just 3 CPU/PCIE plugs. My 1200W has 8 of them in addition to the 24 pin and 6 SATA/Molex plugs. If you're running a card that has 3 8 pin connectors, I wouldn't be going with the minimum recommended wattage PSU anyway.

 

[Arkz]

It depends on the specific PSU, but many come with more than just 3 CPU/PCIE plugs. My 1200W has 8 of them in addition to the 24 pin and 6 SATA/Molex plugs. If you're running a card that has 3 8 pin connectors, I wouldn't be going with the minimum recommended wattage PSU anyway.

Minimum recommended should be perfectly fine. They give those recommendations assuming you might have a heavy CPU and other accessories in the PC to give the recommendation a lot of room for error. Someone might be using a 250W CPU, Massive custom loop with big water pumps, and 8 HDDs in there along with some other AIB like a capture card or 4x M.2 card, so recommending a 700W PSU with a 340W 5070XT Nitro+ makes sense for example. But if you're just running a 9800X3D, an NVMe, and the GPU then a 650 would probably be perfectly fine with it.

only thing i can think of is that sli was a thing back and the gpus needed those cables...

Was SLI still something people cared about in 2020? 2016 maybe.

 

[LabRat 891]

Your particular board has that Aux PCIe 8-pin power input, for more-stable +12V to the lower-most PCIe slots (important for cards that pull the full 75W slot power, or more)

This is true, but they both go onto the same connectors on the power supplies. This one from ASUS only has 3 of them, for instance (they definitely expect you to be using the new connector instead).

View attachment 390479

One could 'safely' split / use 2x PCIe 8-pins off each of a particular PSU's PCI-E/CPU proprietary modular power outputs.

The 'safer' bet would be to get a +12VHPWR/+12V2x6 to 3x Male 8-Pin PCIe power cable.
(Double-check, but any ATX PSU w/ +12VHPWR/+12V2x6 should have standardized +12VHPWR/+12V2x6 pinout directly out of the PSU)


EPS +12V and PCIe 8-pin are both 8pos pin-arrangements of +12V and Ground.

CPU EPS 4+4/8-pin is rated for 300W - fully utilizes 4x +12V conductors, and 4x Gnd conductors.

CPU +12V 4-pin is rated for 150W - fully utilizes 2x +12v conductors, and 2x Gnd conductors.

PCIe 8-pin is rated for 150W - utilizes 3x +12v, and 5x Gnd conductors. (by PCI-SIG spec, all 3x +12v may be drawn from, but only 3/5 of the Grounds are spec'd to carry current.)

PCIe 6-pin is rated for 75W - utilizes 2x or 3x +12V, and 3x Gnd conductors. (by PCI-SIG spec, only 2/3 +12Vs can be expected to carry current, and only 2/3 of the grounds may carry current.)

+12VHPWR/+12V2x6 is rated for 150 to 600W (450W-600W being common on PSUs).

Apologies to the colorblind like myself,
Both pins 4 and 8 on the "PCIe 8 Pin" are connected to Gnd.
Pins 7 and 4 are "Sense" pins. PCIe power "Sense" connections are 'dumb-indicators' for whether a 6-pin (75W) or 8-pin (150W) lead is connected. They are not specified to carry current.

Important to note: EPS and PCIe 8-pins are mixed-inverted polarity of each other.
If one manages to forcibly insert one where the other belongs, hardware will die (possibly everything), PSU included. OCP and other 'protections' may / may not try to save your hardware.

The connector is supplemental, op should try it without using it and i only believe its for heavy overclocking anyway

I have read/experienced* (anecdotally, w/o confirmation(s)) that some boards may experience peak-performance or stability issues if all CPU power receptacles are not fed. -But, only on the highest-TDP SoCs.

*Magically, after I re-built and re-cable managed my case, (1 re-build/cleanout ago) my anomalous 5800X3D instability disappeared (no issue w/ 5600, same PSU, same board).
Only thing I consciously changed, was plugging both my EPS 8-pin and the CPU+12V 4-pin in.

My research/theory goes, that some boards may lay out the traces to the CPU power stages w/ the expectation of all pins being fed. Dunno for sure.

 

[Knight47]

But after browsing around for a little bit, all power supplies come with max 5 slots!

RM1000X has 6 +12V2x6.

There are PSU's with 8 or even 10 if you need.