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PCIe slot shenanigans

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Nimblor

Member
Joined
Oct 2, 2003
What is the deal with the misleading PCIe slot information on data sheets? It is extraordinarily tedious to have to look at manuals to figure out what the slots are actually running at.

I am looking for a motherboard that has a 1 PCIe 4.0 or 5.0 x 16 slot for a graphics card AND a 3.0 x 4 slot for 10gbe nic. PCIe3.0+ (or higher) x8 slot would be better for other peripheral ideas i have in mind but they seem non existent with current boards.

Examples:

MSI
MSI z690-A
SPECSHEET says 3 PCI-E x 16 and 1 PCI-E x 1
MANUAL says PCIe 5.0 x 16, PCIe 3.0 x 4, PCIe 3.0 x 1, and another PCIe 3.0 x 1 -- What the heck is that, certainly not 3 x16 slots.

Asrock
Asrock z690 Steel Legend
SPECSHEET says 1 PCIe 5.0 x16, 1 PCIe 4.0 x16, 1 PCIe 3.0 x16, 2 PCIe 3.0 x1
MANUAL says (PCIE2/PCIE3/PCIE5: single at Gen5x16 (PCIE2); dual at Gen5x16 (PCIE2) / Gen4x4 (PCIE3); triple at Gen5x16 (PCIE2) / Gen4x4 (PCIE3) / Gen3x4 (PCIE5))* * Supports NVMe SSD as boot disks 2 x PCIe 3.0 x1 Slots ---How many x16 slots is that? 1 max.

Asus
Asus Z690-P D4
SPECSHEET says 1 x PCIe 5.0 x 16, 1 PCIe 4.0 x 16, 2x PCI3 3.0x16, 1xPCIe 3.0x1
MANUAL says 1 x PCIe 5.0/4.0/3.0 (!) x 16, 1 x PCIe 4.0/3.0 x4, 2 PCIe 3.0 x 4, 1 PCIe 3.0 x 1

I get that those are the slots and indicate what kind of PCIe card would FIT in the slot, but it is completely useless and makes the shopping process so tedious I can't even stand it. Is there a DB somewhere with current motherboards and actual PCIe performance specs?

/rant
 

Blaylock

"That Backfired" Senior Member
Joined
Jun 5, 2013
Location
Go Blue!
Agreed. This is something that I always found deceptive at best. On sales pages they are generally referring to the physical size of the slot rather than the generation/bandwidth.
 

notarat

Member
Joined
Nov 11, 2010
I have to concur. It's frustrating to have to deep dive user manuals and specs documents to ascertain the information you need to make an informed choice.
 
Joined
Dec 13, 2005
Just double checked, Newegg lists both the physical spec and electrical spec of PCIe slots in the specs tab of motherboards, but weirdly it doesn't let you search by the electrical spec. At least not on the mobile webpage.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
I don't know... I've always separated church and state when it comes to PCIe slots and bandwidth. I certainly wouldn't call it it deceptive, but I would say it got more complicated over the past few years. With the advent of M.2, prior to that, I don't recall much in the way of SB lane sharing (maybe U.2, but that's rare on desktop-class boards).

Think of it the other way around... list something at PCIe X.0 x4 but it's a full-length (x16) size slot. How would you know the actual size of the slot (or better if a GPU can use it - this is an acceptable amount of bandwidth for Crossfire....)? The size of the slot and bandwidth allocated to it electrically are different things. You can have a x16 size slot with x4 bandwidth. The size of the slot is the maximum amount of lanes on it (and physical size). But, every motherboard is different as to how it allocates the bandwidth and which physical slots get how much (how it's connected electrically). Past mobo reviews showed the back of the motherboard to show how it was connected electrically.

The motherboard website, specifications page, all list the size and bandwidth of the PCIe slots. Often, they tell you if it bifurcates or shares lanes with XXX. If you want to know how they split lanes when things are attached to the motherboard, that's a deeper dive into a manual... which makes sense since so many are different. I honestly don't know where would put this information more front and center... FTR, the back of boxes state this, typically, as well so.... it's there for all to see.

Example:
Intel® 12th Gen Processors*
2 x PCIe 5.0 x16 slots (support x16 or x8/x8 modes)**
Intel® Z690 Chipset***
1 x PCIe 4.0 x16 slot (supports x4, x4/x4 modes)
* Please check PCIe bifurcation table in Chapter 1.
** When ROG Hyper M.2 card is installed on PCIEX16(G5)_1, PCIEX16(G5)_2 will run x8 only and if ROG Hyper M.2 card is installed on PCIEX16(G5)_2, PCIEX16(G5)_1 will run x8 only.
This is Asus... shows the max bandwidth\size, and actual throughput (electrical) of each slot. Since there is some lane sharing with the AIC for M.2 it shows lane sharing. You see that on storage as well (not always).

MSI
MSI z690-A
SPECSHEET says 3 PCI-E x 16 and 1 PCI-E x 1
MANUAL says PCIe 5.0 x 16, PCIe 3.0 x 4, PCIe 3.0 x 1, and another PCIe 3.0 x 1 -- What the heck is that, certainly not 3 x16 slots.
It certainly is... 3x x16 slots... Three full-length slots. The specs say that one slot is 5.0 x16, the second slot 3.0 x4, and the third 3.0 x1 along with an actual 3.0 x1. That matches.

From MSI specs page below.

  • 3x PCIe x16 slots
    • PCI_E1 (from CPU)
      • Supports up to PCIe 5.0 x16
    • PCI_E3 & PCI_E4 (from Z690 chipset)
      • Supports up to PCIe 3.0 x4 & 3.0 x1
  • 1x PCIe 3.0 x1 slot (from Z690 chipset)

Asrock z690 Steel Legend
SPECSHEET says 1 PCIe 5.0 x16, 1 PCIe 4.0 x16, 1 PCIe 3.0 x16, 2 PCIe 3.0 x1
MANUAL says (PCIE2/PCIE3/PCIE5: single at Gen5x16 (PCIE2); dual at Gen5x16 (PCIE2) / Gen4x4 (PCIE3); triple at Gen5x16 (PCIE2) / Gen4x4 (PCIE3) / Gen3x4 (PCIE5))* * Supports NVMe SSD as boot disks 2 x PCIe 3.0 x1 Slots ---How many x16 slots is that? 1 max.
Three full-length slots and two x1 slots. The specs say PCIe 2 (second slot from the top) is 5.0 x16 bandwidth. While dual runs 5.0 x16 and 4.0 x4 in the PCIe 3. If three slots are in use, the third is 3.0 x4. From the Asrock specs page...

- 3 x PCIe x16 Slots (PCIE2/PCIE3/PCIE5: single at Gen5x16 (PCIE2); dual at Gen5x16 (PCIE2) / Gen4x4 (PCIE3); triple at Gen5x16 (PCIE2) / Gen4x4 (PCIE3) / Gen3x4 (PCIE5))*
- 2 x PCIe Gen3x1 Slots
- Supports AMD CrossFire™

Asus Z690-P D4
SPECSHEET says 1 x PCIe 5.0 x 16, 1 PCIe 4.0 x 16, 2x PCI3 3.0x16, 1xPCIe 3.0x1
MANUAL says 1 x PCIe 5.0/4.0/3.0 (!) x 16, 1 x PCIe 4.0/3.0 x4, 2 PCIe 3.0 x 4, 1 PCIe 3.0 x 1
This tells me there are four full-length slots. One runs 5.0 x16, the second 4.0 x4, and two at 3.0 x4. Finally the 3.0 x1 slot.

From the Asus specs page...


Intel® 12th Gen Processors*
1 x PCIe 5.0/4.0/3.0 x16 slot
Intel® Z690 Chipset**
1 x PCIe 4.0/3.0 x16 slot (supports x4 mode)
2 x PCIe 3.0 x16 slots (support x4 mode)
1 x PCIe 3.0 x1 slot


In short, the specs page tells you. No need to go into the manual for some of that stuff.
 
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OP
Nimblor

Nimblor

Member
Joined
Oct 2, 2003
I think that could be cleared up by the *crossfire ready* or equivalent endorsement. Doesn't that tell you what you need to know?

It gets even wilder with the AMD systems and the throughput variations with the different cpu/apus and preference to use the names like Matisse vs the models.

All of that being said, within the same brand like Asrock, the workstation/server motherboards seem much more upfront and clear about the throughput vs connectivity. I am not sure if they are just simpler designs or if the communication is more precise.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
Noting Crossfire support, I'm not sure how that would help. If the specifications aren't clear, I wouldn't expect that person to know that Crossfire needs an X4 slot (Nvidia SLI min. is x8).

These are really pretty clear to me...The examples show you the slot size and explain its connectivity. If you know that cadence, it should be straightforward.

I agree 100% AMD is more convoluted. More lanes to share... more CPUs to share...I have to read those more than once for sure, lol! The intel ones, pretty easy peezy.
 
OP
Nimblor

Nimblor

Member
Joined
Oct 2, 2003
I'm going to bring this rant to a close here, but consider the following.

  • Lightning Fast Experience: PCIe 5.0 slots, Lightning Gen4 x4 M.2, USB 3.2 Gen 2x2
Slots? How many PCIe 5.0 slotS are on that board again?

After clicking on the specifications tab I note that it does not include the electrical connectivity or the number of 5.0 slots, but there are 3 PCIE x 16 something. Let's check the details tab off of the product specifications page. Looking for 5.0 slotsssss, it appears to be 1. Now I am 3 pages deep in the website and irritated.

Perfectly clear, and irritating. All of that glorious motherboard pron on the front page, but 2 clicks later I feel dirty and ashamed.
 
Joined
Dec 13, 2005
You're trying way too hard, my man.

Newegg

Specs page -

PCI Express 5.0 x161 x PCI Express 5.0 x16

* Actual support may vary by CPU.
PCI Express 3.0 x162 x PCI Express 3.0 x16

* Supports up to PCIe 3.0 x4 & 3.0 x1
PCI Express x11 x PCI Express 3.0 x1
 

Blaylock

"That Backfired" Senior Member
Joined
Jun 5, 2013
Location
Go Blue!
What I mean by deceptive is the naming mostly. If a slot is named PCIe 3.0 x16 you can't know what the bandwidth is, only the slot size. I understand that there are a ton of variables at play and it's not really possible to simplify it (especially now). I also admit that years ago I didn't understand that there was a difference between physical size and bandwidth. I just assumed a x16 slot had x16 bandwidth. There are certainly far more people who don't understand it than those who do.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
Slots? How many PCIe 5.0 slotS are on that board again?
That's a clear typo.... what can you do? The specs are accurate and tell you exactly what each slot does.

After looking at mobo boxes, most show the same thing (size and bandwidth)

Yeah, this isn't rocket science, but it also isn't your abc's and 123's, lol.

Now I am 3 pages deep in the website and irritated.
Seriously? Once to get to specs page, two to click on details is too much? Brotha..... can't help that....yikes. worth noting, the other specs pages don't have an extra click to see details.... and again, the electrical is there on all of them. Literally one click on mkst vendors and the info is there. No manuals... just on the specs page.

You're trying way too hard, my man.
Or the board's spec pages are pretty clear.

I guess 'deception' just has too much of a negative connotation. Confusing yes, but intentionally deceiving, I dont see why.
 
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OP
Nimblor

Nimblor

Member
Joined
Oct 2, 2003
But how will we ever find all the motherboards with PCIE x 16 slots that run at 3.0 x 1 for all of my 3.0 x1 cards that I need a PCIE x 16 slot for? :rolleyes: One mobo at a time. The same way you have to see if they have a 3.0 x8 electrical in an 8x or 16x slot. I think it should be the other way around. Throughput spec as primary front facing shared info, and searchable, with slot types buried in the details. Just my thoughts.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
But how will we ever find all the motherboards with PCIE x 16 slots that run at 3.0 x 1 for all of my 3.0 x1 cards that I need a PCIE x 16 slot for? :rolleyes: One mobo at a time. The same way you have to see if they have a 3.0 x8 electrical in an 8x or 16x slot. I think it should be the other way around. Throughput spec as primary front facing shared info, and searchable, with slot types buried in the details. Just my thoughts.
Any x16 slot will do for your example though. Note it's literally the same effort as the current way, right? Worth noting, there's also a contingent of people that don't know an x1 size card works in x16 size slot. So there's that consideration too.

Really, just get good at translating the specs as, again, all the information is already there (physical and electrical). Literally 1 click away (2 if you're msi). Nothing is buried in manuals (outside of some lane sharing deets with storage that typically - but sometimes - has nothing to do with PCIe lanes) and it's all there on a specs page for you to see... one motherboard at a time regardless if it's physical or electrical first.

Like, where do you get specs and detailed information if not the specs page and manual?? I don't know... I guess I just dont agree with this information being shenanigans or hard to find, I suppose. If you want specs, read the specs page. It's not going to be listed in 'features'. :)
 
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