When PCIe x1_3 & PCIe x1_4 are occupied, PCIe x16 run at x2 mode, what if ONLY ONE is occupied?

Happy Hopping

Happy Hopping

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I am just fed up w/ Asus. I bought a motherboard that c/w a few PCIe x 1 slot, and a 2nd PCIe x 16_2 slot (only run at x4 to begin with)

I need that PCIe x 16_2 slot to run a x4 PCIe NVMe adapter

Now, I have 2 other adapter that I need install at PCIe x 1 _3 and PCIe x 1 _4 (a sound card and a USB 3 port adapter). So according to the manual, "PCIe x 16 slot shares bandwidth with PCIe x 1_3 and PCIex1_4 slot. When PCIe x1 _3 and PCIe x 1 _4 are occupied, PCIe x16 run at x2 mode

So what if ONLY ONE of the slot is occupied, ie.., either PCIe x 1 _3 or PCIex1_4, but NOT both, does that mean that PCIE x 16_2 slot still run at x2 mode?

also, what exactly is "occupied" means? does it mean it's plug in or does it has to be in use? Because if it's plug in only, it shouldn't use any bandwidth

and how much bandwidth does a sound card use at x1 speed?
 
What does c/w mean?
Occupied means an expansion card is inserted in the slot.
 
c/w = comes with

I don't understand why a card NOT in use, while occupied is still sucking up the bandwidth. Say I have a USB 3.0 slot card, if there is nothing connects to it, why is it sucking up the bandwidth? it's not in use
 
Occupying lanes isn't the same thing as saturating all of the available bandwidth.
 
If there is a powered card that is communicating it’s presence, then the lanes will get allocated to it regardless of whether the lanes are actively being used. PCIe bandwidth is statically allocated, not dynamically.

That behavior is not Asus’s fault, that behavior is simply how PCIe works. But I agree that their manual seems unclear when the slots are not fully populated. What board is it? We can review the manual and board block diagram.

I admit I am not 100% familiar with the protocol, and maybe all it takes is for a ground signal in the comms lane from the card, means even if the card is not powered then it registers as installed and the lanes get allocated. Mostly academic rambling, since nearly all 1x or 2x cards I have ever seen draw power from the slot anyway.

EDIT: There are two “sense” pins on the card, one on the power finger before the key notch, and one on the farthest end of the card finger. The first pin (PRSNT1#) sends a 12v signal to the motherboard indicating the slot is populated. The second pin (PRSNT2#) indicates the slot bandwidth, but that only means anything if the slot can provide the full bandwidth. If the slot cannot provide the full card bandwidth, then I think everything defaults to 1x speed. Depends on the card it appears.

In any case, the moment you plug in a card, even if you are not using it, the MB will statically allocate bandwidth to it. Using it does not matter, if you install the card the MB assumes you will use it.
 
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This isn't going to be specific to Asus. Every board has essentially the same PCIe lane allocation since they are using the same CPUs and chipsets.

It sounds strange, but if you actually want to fully populate the PCIe slots, you have to go HEDT.
 
Martin, it's the Asus B250H Strix Gaming motherboard. I never look into this, as I never use a lot of PCIe slot. The previous PC has a lot of slots, so I don't think I have this problem (it was a top notch Asus dual CPU workstation motherboard). With this new PC, it's still the same 3 cards (video, sound card, NVME adapter card), and I just add a USB 3 card, but can find a USB port cable to directly connect to the motherboard

which goes back to my question: Asus said if BOTH x1 slot are occupied, I get x2 speed on my x4 lane, what if only 1 PCIE slot is occupied? do I still get X4 speed or down to x2?
 
You might want to verify that if there's any onboard components using PCIE, you can turn them off to give more lanes to add-on cards.
 
Happy Hopping said:
which goes back to my question: Asus said if BOTH x1 slot are occupied, I get x2 speed on my x4 lane, what if only 1 PCIE slot is occupied? do I still get X4 speed or down to x2?
Click to expand...

You'd probably need to try it and see. My guess would be using either slot will do it, but maybe there's something else that gets x1 if you use one slot and x2 if you use zero or two.

This could easily be non-native english; combining when slot A is occupied, bandwidth is x2 and when slot B is occupied, bandwidth is x2 to when A and B are occupied, bandwidth is x2. They did the same thing with m.2_1 and the first two x1 slots.

There's not really that many lanes on desktop processors and it's circuit switched and making allocation flexible is expensive (tricky wiring or fancy pci-e switch chips or both are required). So the tradeoff is you get a lot of slots, but you can't use them all at full capacity.
 
Here is the problem with your motherboard’s chipset:

It has only 12 total PCIe lanes. Period. And in the case of your motherboard, there are several onboard devices such as audio that eat up some of the chipset’s meager 12 lanes right off the bat. (I did not include the primary PCIe x16 slot as that comes directly off of the CPU rather than the chipset.)
 
Most likely, yes the PCIe 4x slot would move down to 2 lanes with either of the 1x slots in use. From my understanding of what I read, the 4x and two 1x slots share the same four lanes.
 
You an always just install things and see how it works. There's ways to check how many lanes everything is using once you have them installed. I had to physically move some stuff around to get all of my NVME drives working at 4x speed on my motherboard.
 
I'm really glad my motherboard never disables lanes for any reason.
 
See my prev. motherboard is 8 slots, but that's a $600 motherboard. So I thought I don't need a $600 motherboard, and so, I bought this $120 motherboard.

Anyhoo, what's done is done: to cut to the chase, does a NVME drive, w/ R/W at 3.4/ 3.0 Mb/sec

https://www.crucial.com/ssd/p5/ct1000p5ssd8

1) do we really need X4 speed

2) at what file size that we require x4 speed? for e.g., if I only open a 4MB file, then I assume we can't tell a difference

So say a 8GB file size is un-rar from 1 NVME to another NVME, do we need a 4X PCI E lane speed?
 
Some of us aren't dealing with 4MB files, just today I had to transfer and copy over 280 gigabytes, (with a redudancy as well, just to be safe.) 4X NVME, even my stupid expensive GEN4 NVME, made a pretty big difference in the amount of time it took.

Today also made it very clear of the limitations of TLC NVME SSDs for me, but that's getting WAY off topic of PCI-E lane discussion.
 
hey, both of my SSD are 500GB full. That's why I bought 2 new SSD at 1 TB. So when I do file back up, I just let it do the transfer in the back ground to ext. USB 3.0 hard drive. It probably takes longer, but the USB 3.0 limitation is even slower, so if it's a back up file transfer of 500Gb, it doesn't bother me

What I need is the fast ability to un-rar a 8GB file from 1 drive to another. But w/ the new 1 TB drive I got, I can un-rar it w/i the same drive.
 
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