PCIe 4.0: 300W of slot power (or not) and double the bandwidth!

August 25 Update: Tom’s Hardware was told incorrectly and they’ve updated their article. The maximum slot power will continue to be 75W as it is currently with PCIe 3.0 but the total allowed power could maybe increase. The extra wattage will still come from PCIe power connectors on the card like it is today.

Tom’s Hardware had the opportunity to chat with Richard Solomon, VP of PCI-SIG (the group responsible for the PCI Express standard), about the upcoming PCI Express 4.0 standard. The new standard is still a work in progress but they’re expecting to finalize it by the end of the year.

Check out the article for all the details but the two main takeaways is that the bandwidth doubles, from 16GB/s with 3.0 x16 to 32GB/s with 4.0 x16, and the power available from the PCIe slot increases from 75W to a whopping 300W! And that’s the minimum, the spec isn’t finalized and it could maybe even end up as high as 400-500W!! This is great news for SFF because one constant headache for really small cases is the tendency of GPU makers to put their PEG power connectors on the top edge of the card, increasing the necessary width of the case. The AMD Radeon Nano bucked that trend and put the power connector on the front edge of a flagship card but then AMD regressed with the RX 480, the reference version of which has the power connector back at the top.

With the motherboard delivering at least 300W from the slot that should negate the need for power connectors on the card for all but the highest end of GPUs. The downside though is that power has to come from somewhere and the existing 24-pin motherboard connector cannot handle that amperage and unless Intel has a modernization of the ATX spec planned that they haven’t told anyone about, the only solution is to move the 6 and 8-pin PCIe power connectors from the video card to the motherboard. So the same amount of cabling will be needed but at least SFF cases will no longer need to account for anything other than the width of the video card’s PCB/shroud itself.

One worry I have about this development though is that flagship Mini-ITX motherboards are crowded enough as it is. Having to make room for possibly two extra power connectors plus the traces and circuitry to handle 300W of power to the slot could be difficult and my concern is that motherboard manufacturers will put more of their effort into ATX since there’s much more room to work with there. It could be a boon to the microATX form factor though which seems neglected as of late.

We’ll just have to wait and see, while the spec will be finalized in the relatively near future it will still take a year or two for motherboard manufacturers to implement it and for the new standard to become ubiquitous.


One more thing real quick, there is an external cabling standard called OCuLink that has been in the works for some time. It is a x4 cable, currently specced for PCIe 3.0 but this slide suggests that there’s room to scale up to PCIe 4.0 in the future. If it ever sees the light of day it would be a huge boon to those building external GPUs boxes so they would not have to rely on the availability of Thunderbolt 2/3 connections to do the same thing.

Thoughts? Discuss them in the forum here.