E-ATX Motherboard in ATX case

PhilGQ · Friday at 22:13

Hello guys

I have been eyeing up this motherboard to move to AM5: https://www.overclockers.co.uk/asrock-x870e-taichi-lite-socket-am5-ddr5-eatx-motherboard-mot-asr-03304.html

I want a board with two PCIe 5 16x slots, this is the cheapest. However, its E-ATX.

From what I have read the screw alignment is all the same as ATX. The implication being that provided the case has the physical space, it will fit. The caveat being there won't be any support for the overhanging bit, so would require more care when plugging in anything into that part.

My question is, is my understanding correct? I have an old Antec P110 case, which I'd be happy to reuse in this build, it seems to have bags of space beyond the end of the current motherboard.

Tetras · Friday at 22:20

PhilGQ said:
I want a board with two

You're aware that no AM5 board has two PCI-E full length slots with 16 lanes electrically, right?

PhilGQ said:
From what I have read the screw alignment is all the same as ATX.

Yes, they mirror ATX on the part that's the same dimension.

PhilGQ said:
The caveat being there won't be any support for the overhanging bit, so would require more care when plugging in anything into that part.

Yeah, but the Taichi doesn't look like it has any anyway.

PhilGQ said:
I have an old Antec P110 case

I'd measure it, to make sure nothing snags.

PhilGQ · Friday at 22:31

Tetras said:
You're aware that no AM5 board has two PCI-E full length slots with 16 lanes electrically, right?

No I wasn't aware of that, doesn't that kind of defeat the object then? Or is this only an issue for power and not bandwidth.

My plan was to give me the potential to have two GPUs for video editing and/or AI. Not now, but at some point in the future, when I have more money.

Tetras · Friday at 22:40

PhilGQ said:
No I wasn't aware of that, doesn't that kind of defeat the object then? Or is this only an issue for power and not bandwidth.

Power is an awkward one, I wouldn't like to guess. Though, boards that expect you to use multiple graphics cards (or are aware of the possibility) I'd expect to be capable of providing enough power to the slot.

Bandwidth, yes, that's an issue, but it depends on your workload and the specific card(s) used. The best that you'll get on any AM5 board is a 8/8 lane split between the two slots and I believe that's what the Taichi does.

PhilGQ said:
My plan was to give me the potential to have two GPUs for video editing and/or AI. Not now, but at some point in the future, when I have more money.

I'm not sure if the reduced bandwidth would have any impact for those tasks. For gaming, it mostly matters only when the VRAM is exceeded. If you were to buy two cards that were electrically 8 lane, then there's no issue there.

PhilGQ · Friday at 22:58

Hmm, sound like I would be better to assume I'll stick to the best single card solution. I can choose a slightly cheaper motherboard and not need to worry about the E-ATX thing at all then.

Thanks for your replies, glad I didn't go off half cocked. There was a time when I would have been aware of this!

jigger · Saturday at 18:44

A tr3 Threadripper might be worth considering. That gives you PCI-E out the ears.

PhilGQ · Saturday at 23:02

jigger said:
A tr3 Threadripper might be worth considering. That gives you PCI-E out the ears.

Not sure I have the budget, I suppose could look at used if I went that way.

PhilGQ · Saturday at 23:10

I had another though, re-reading Tetras' replies and doing a bit of research.

The motherboard I suggested above only has two 16x slots and nothing else (not counting the m.2) but the two 16x slots do this 8x8 thing. Does that mean if you stick any other 1x card (eg sound cards / Network card) in the spare slot it reduces the bandwidth to the GPU to 8x, or is only if there's another 8x/16x card in the slot? If so it seems like a design weakness.

HoneyBadger · Sunday at 00:25

In your scenario, it would reduce to 8x.

The board, with a 9000 series CPU, forgiving any m.2 will provide 16 lanes.

So that’s either
PCIE1 at x16

PCIE1 at x8
PCIE2 at x8

If you were put a nic or sound card in PCIE2, the GPU in PCIE 1 will drop to x8, the other slot will have x8 even if you put in a x1 or x4 expansion card.

Gone are the days of PLX chips on motherboards, complimenting CPU lanes.

The real question here would be are you goi g to fully maximise even x8 PCIE Gen5 lanes if running 2 GPU’s. If so, you’ll need to go thread ripper or the like to provide you with the number of lanes you’d require.

Tetras · Sunday at 00:32

PhilGQ said:
I had another though, re-reading Tetras' replies and doing a bit of research.

The motherboard I suggested above only has two 16x slots and nothing else (not counting the m.2) but the two 16x slots do this 8x8 thing. Does that mean if you stick any other 1x card (eg sound cards / Network card) in the spare slot it reduces the bandwidth to the GPU to 8x, or is only if there's another 8x/16x card in the slot? If so it seems like a design weakness.

Yeah, is a bit of a 'mare with modern boards if you want to use multiple slots, they really don't want you to.

The Creator used to be good with this (slot config), not sure about the current gen though. It is also still subject to the same CPU/chipset limitations, so you won't get extra lanes.

Awhile back there were boards with a PCI-E 1 lane slot positioned above the primary graphics, which was handy for wifi, sound, etc, but M.2 slots seem to have ended that.

jigger · Sunday at 11:27

PhilGQ said:
I had another though, re-reading Tetras' replies and doing a bit of research.

The motherboard I suggested above only has two 16x slots and nothing else (not counting the m.2) but the two 16x slots do this 8x8 thing. Does that mean if you stick any other 1x card (eg sound cards / Network card) in the spare slot it reduces the bandwidth to the GPU to 8x, or is only if there's another 8x/16x card in the slot? If so it seems like a design weakness.

That’s going to depend on the topology and how the manufacturer has configured the motherboard and if the BIOS has any bifurcation options.

Edit: Depending on the performance of the card/cards you want to use, 8x PCI-E gen5 (32GB/s) could offer plenty of bandwidth. The lower end RTX pro cards are 8x and they offer near 25 tflops. Nvidia don’t move to 16x until close to 50 tflops.

PhilGQ · Sunday at 20:01

It’s starting to make a bit more sense now, I was wondering what the point of the extra lanes on the x870E was over non E if the boards don’t support devices, but it looks like the extra lanes are gen 3 or 4 PCI-E.

There does seem to be some boards including B850 which have extra 1x or 4x slots, which I guess might be better if I knew I was going to use them. I suppose I need to make the decisions based on whether there’s more chance of dual gpu or other misc expansion cards.

Tetras · Sunday at 22:37

PhilGQ said:
but it looks like the extra lanes are gen 3 or 4 PCI-E.

Yeah, there's no PCI-E 5.0 from the chipset lanes.

Ryzen AM5 CPUs have:
- 16 PCI-E 5.0 lanes for the graphics (can be split to 8/8).
- 4 for a PCI-E 5.0 M.2 slot.
- 4 more, which are often used for USB4 on X870/X870E or a PCI-E 5.0/4.0 M.2 slot on B850.