Planning on Building My Own PC - Have Questions about PCIe x16 GPU Slots


#1

Hi

I tried finding an answer to this one but I failed.
I am planing on building my PC soon so I started doing research on what components to buy, prices to compare and so on, I already decided the CPU option, and now it’s time to compare which motherboard should fit my needs, The offer is huge and is rather hard to find the best choice and ballance between price and features.

And so searching for one I came accross a concern about something,
For the sake of conversation, the PC will be devoted mostlly to gaming, not 4k HDR or anything that fancy, but a regular gaming at 144Hz* @ 1440p or so.
*This is the monitor I intend to use, the fps rate doesnt have to be 144 though a 60fps should suffice.

The processor of choice is AMD Ryzen 5 2400g with VEGA graphics, I am looking to get some buget friendlly configuration.

But back to my question, so, as I searched for a motherboard with AM4 socket for mentioned CPU, most of them are multi-GPU which means they have 2 PCIe x16 ports for GPUs, but I don’t intend to use both of them, maybe only one port after a while. so there will be one unused port at any given time, my concern about this is: Will that second unused port slow down my GPU installed in other port?

Because since there are two ports the total number of PCIe lanes from the CPU is devided between them, so half of them will never be actually used, my GPU would work at only 50% of it’s pottential due to that reason, since insted of getting all 16 lanes each port gets only 8 lanes.

Maybe I am wrong about this nevertheless I am concerned whether or not this theory is true.

BTW: I could use some recomendations about which motherboards to buy, or other components for that matter.

Here is what is important to me for the motherboard to have:
at leats 2xUSB 2.0 on back
at least 2xUSB 3.1 Gen1 anywhere
any number of USB 3.1 Gen2 anywhere
at least one HDMI connector on the back (I coud use two actually (one can be a DisplayPort))
support of achiving 144 HZ from integrated VEGA GPU (some motherboards only
support 60 Hz)
Dual-Chanel memory up to 32 GB or more max. (4 slots)
at least one m2 slot (could use one but is not so important)
any number of SATA connectors
any number of PCI expansion slots
overclocking capabilities are not that important

So here are some data if you have a recomendation feel free to share it.

Thanks in advance
Best Regards


#2

No.

It doesn’t really work that way… if nothing is in the PCI port, then the CPU just ignores it. It’s not slowing the rest of the system down merely by existing.


#3

Thank you for clarifying this. But there can be only a limited number of PCIe lanes supported by the CPU and thus the motherboard is spreading them accros all PCIe slots, so if there are two of them and the maximum number of supported lanes by the CPU is 16 than each gets only 8 (8x2=16), thus creating a bottleneck in the PCIe bus, which in turn slow down GPU performance, unless of course the maximum number is 32 in which case both get maximum number of lanes. (Well please correct me if I am wrong I am just assuming how this work, I dont want such things to cripple my PC in the future, so I want to be sure what to look for and what to avoid).

Thanks


#4

You don’t have to worry about a bottleneck on the GPU, that would be the least of your worries…

It is unrealistic to use a Ryzen 2400g at 1440p, let alone hoping to get 144Hz out of it. It was really designed for 720p, or 1080p at most.

If you intend to game at 1080p at around 60Hz then the 2400g would be realistic, but if you really want to go to 1440p anything, then I would recommend getting the Ryzen 2600 and a dedicated video card instead.


#5

Yes, if you have two PCIe video cards plugged in, the CPU will split the lanes between them, giving you two PCIe x8 slots. But if only one card is plugged in, then that slot will get all 16 lanes.

However, I’d bet that without using dedicated benchmark tools, you wouldn’t see the difference between an 8x and 16x video card. Most of the time, the bus isn’t being exercised; the only time you really see the bus pushed hard is during the initial load of textures, shaders, and geometry. After that, the bus only gets used to update the position of objects already in the vertex buffer.

Honestly, of all the things to worry about when picking a motherboard, the number of lanes going to the video card slot really isn’t something to worry about.


#6

Well I meant 1080p actually sorry for that.


#7

Thanks for clarification, I understand now.

Now what should I be worried about in fact?


#8

Nothing at this point. Just choose a motherboard that has the connectors and RAM sizing you want, and you’ll be fine. Building a computer is not brain surgery so don’t overthink it.


#9

It would be a good idea to verify your parts are compatible with pcpartpicker.com so you can be assured you won’t run into any surprises in that regard.


#10

Don’t buy too small an SSD for your boot drive… :slight_smile:

I’d suggest at least 500GB drive, but if you game I’d say get a 1TB drive. If you buy too small a drive, you’ll end up playing “the space game”, which is really annoying.


#11

I am well aware of that, now I have a laptop with 120 GB SSD for 3 years now, and I started playing that “game” 2 years ago.

as for storage I plan on using M2 SSD or NVMe for booting (win10) I estimate that i will need 256 GB for that (I plan on storing only system vital files here, drivers, things like that and basic programs.

For everithing else I plan on buying 512-1024 GB SATA SSD.

Anyway Thank you for helping me alleviate my concerns about all this.

Best Regards