T3600- 8HPGT PCIe3x16 specs

Question

I'd like to install a PCIe to M2 adapter in my T3600. There are two x16 ports on the 8HPGT, but I would have to install the adapter in the top slot to keep from totally blocking my GPU fan.

I can't find information on whether or not the second x16 is still connected directly to the CPU or if it runs through the PCH.

I don't want to strangle my GPU bandwidth, and if I have to, I guess I'd rather run the M2 adapter through an x4 port. Just wondering if that's what it'll come down to.

sam55todd · Accepted Answer

Upper PCIe slot has only x4 PCIe lanes which is exactly what is needed for single M.2 NVMe drive.
Chipset/PCH has PCIe Gen2 standard (x8 lanes) while CPU normally has faster PCIe Gen3 version

There's a hardware detection program called HWINFO64 which can show you a tree-map of your PCI-e bus devices like this (it's not T3600 machine)

As you can see on segment marked as (A and B) - NVidia card and M.2 storage device are connected directly via CPU (Rocket Lake CPU) PCI bus and device C is connected via PCH PCIe lanes (SD card-reader).
HWInfo64 can also show you info on slot capabilities (maximum link supported) and device information used on that slot (current link speed and lanes used).

As for adapter card detection mentioned by @Chino de Oro I don't think it matters as PCIe lanes wiring is pretty much standard 1-to-1 connection pinout (4 pins for each PCIe lane - Rx and Tx signal pairs {in and out, or + and -}) but the problem might be if it has extra controller on board (which for M.2 NVMe adapters is hardly a case except for RAID or hardware level active-type bifurcation) - then it's up to CPU and BIOS to decide whether to allow PCIe to work (on consumer products Intel has designed some architectures the way for CPU PCIe lanes to work only with Storage and GPU devices, Dell is normally adding extra layer of restrictions via BIOS to limit what kind of cards can be inserted there, this might be the case since blue PCIe port on your motherboard is said to be for GPU in Dell manual).
If your adapter is x16 PCIe with x4 NVMe M.2 cards then slot should support PCIe lanes bifurcation (automatic or manual configuration via BIOS, on server boards there are normally options like Auto, x16, x8x8, x8x4x4, x4x4x8 , x4x4x4x4).

But I guess (as per your link to adapter) you're using single slot M.2 adapter therefore most of above won't matter anyways, especially considering what T3600 is more of a server-grade platform with much less restrictions on PCIe devices used and NVidia GTX 1060 being a lower-end card with very limited actual bandwidth requirements (GB/s) for PCIe width (therefore x4 lanes is normally not a bottleneck).

Chino de Oro · Answer

It doesn't matter if you are going to use x16 slot or x4 slot for the M.2 adapter, your GPU doesn't share any bandwidth with any other slot, so it won't be affected by it.

Your concern should be with the M.2 adapter. Would it work for your purpose.

WilliHu · Answer

The slot that I use would absolutely matter. A 3x4 slot is restricted to less than 4gb/s, while an NVMe M2 can have theoretical transfer speeds of up to 20 gb/s, though the 3x16 slots on my motherboard are only capable of ~16 gb/s.

My question specifically is whether or not the second x16 is still connected directly to the CPU or if it runs through the PCH.

WilliHu · Answer

I wasn't certain if I would receive a quick response to my question, so I decided to run benchmarks to test for any major changes to performance. Whether or not it was an effective method, I have no idea.

Out of 6 separate tests using a GTX 1060 6gb, I discovered consistent but minimal increased performance with the upper port, with one outlier.

Test 1- Lower: 55.7

Test 2- Upper: 56.1

Test 3- Lower: 54.4

Test 4- Lower: 54.8

Test 5- Upper: 55.2

Test 6- Upper: 55.5

With this information I am not as worried about performance loss. I don't have any absolute answer, and if anyone does it would still be appreciated.

Chino de Oro · Answer

As I mentioned earlier, the M.2 adapter should be your concern and you also did not provide any info for M.2 adapter used. Until you can verify if the M.2 adapter even work with M.2 storages and providing a test result from both slots, discussion of theory or practical performance is moot.

Same response for your GPU and you could see from your test. There is no sharing bandwidth and you got similar performance from either slot. Since you did not accept the response and running test yourself. But your test result is pointless without the other x16 slot running some large data transfer from an M.2 storage for testing purpose. You still don't know if a use of M.2 would affect the GPU bandwidth or not.

WilliHu · Answer

Scratch that, I see your point. The adapter I listed previously only uses four lanes while being compatible with an x16 slot.

WilliHu · Answer

https://a.co/d/dwTRbwl

This is the adapter I intend to use.

I'm not worried about whether or not the M2 adapter would interfere with GPU bandwidth, like I said earlier I just needed to know if the second PCIe slot ran through the PCH, as the PCH would limit bandwidth to 4gb/s from what I've found.

Chino de Oro · Answer

For what it's worth, your board's PCIe slots are wired direct to CPU.  If you are using passive adapter as linked, it will give you access to 4-lane for storage only.  To make use of PCIe x16 slot, a bifurcation card will give access to all 16-lane of bandwidth, but considered the cost, it's not worth it.

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T3600- 8HPGT PCIe3x16 specs

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