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I am trying to find something that is exceptionally weird and bizarre. I want to use a M.2 NVMe x4 SSD in a PCI-Express x1 slot.

x4 NVMe SSDs directly use PCIe bus protocol, and so can be directly plugged into a full-size PCIe slot using a simple passive adapter. But there are four data lines, so these passive adapters are virtually all x4 lane cards.

By specification, all PCIe cards are backwards compatible with the lowest bandwidth x1 lane slots. If the x1 slot is designed with an open end, it is possible to plug a x16 card into it with 15 lanes hanging exposed in midair and unconnected, and it will work. It won't work well but it will work.

So, what I need is a NVMe x4 passive adapter card, which will plug the M.2 into a normal PCIe x1 slot, and leaves the remaining 3 lanes unconnected.

I have been searching the web on and off for months and have not found anything like this yet.

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After doing some more hunting with weird search terms, I have found a solution in the Amazon Marketplace:

https://www.amazon.com/NGFF-PCIe-Adapter-Samsung-SM951/dp/B01MS64UBB

US$ 34.95 .. a bit expensive for a board with virtually nothing to it, but oh well.

This is the correct non-SATA adapter card, if all it has is the M.2 slot with no chips on the board.

enter image description here

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  • what speeds did you get using the x1 slot vs x4? – malhal Jul 15 '19 at 13:29
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    It varies with the motherboard type, as there are different PCI Express versions. 1.0 1x is 250 MB/s, 2.0 1x is 500 MB/s, 3.0 1x is 985 MB/s, 4.0 1x is 1.969 GB/s, etc. This is faster than the SATA interface for old motherboards. SATA-I is 150 MB/s, SATA-II is 300 MB/s, SATA-III is 600 MB/s. – Dale Mahalko Jul 16 '19 at 16:18
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    I'm aware of the 3.0 1x effective lane speed of 985MB/s I was wondering what you actually got. – malhal Jul 16 '19 at 20:26
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It's amazing how much things have moved on since the OP. PCIe is so versatile. NVMe SSDs are just PCIe devices, which are generally backwards compatible with older PCIe versions or reduced PCIe lanes.

I've successfully used these cheap vertical Cablecc adapters from Aliexpress to run PCIe 3.0 x4 NVMes in a PCIe 3.0 x1 slot:

enter image description here

(Similar items are available from Amazon if you don't want to wait for shipping from China).

Bandwidth is constrained as expected, but still about twice as fast as a SATA SSD:

WD SN550 1TB in x1 adapter in PCI 3.0 slot

The x4 adapters also work fine and avoid the bandwidth constraints (when in a x4 or above slot). In fact I've even successfully used a x4 adapter advertised as PCIe 3.0 to run a Gen 4 drive at full speed in a PCIe 4.0 slot:

WD SN850 1TB in x4 adapter in PCI 4.0 slot

This allows otherwise impossible things like running two PCIe 4.0 x4 SSDs at full speed on a B550m motherboard (moving the GPU into a PCIe 3.0 chipset slot). Windows can even RAID them, not that you'd want to: 2 x WD SN850 PCI 4.0 x4 striped

These are passive adapters so will work even on much older motherboards that don't have native M.2 slots (although you probably won't be able to boot from them, unless you are expert at patching BIOSes). For example, I've successfully run a PCIe 3.0 x4 NVMe in a PCIe 2.0 x4 slot

(Even older laptops with PCIe NGFF slots can in theory host other PCIe devices e.g. an M.2 NVMe SSD with a suitable keying adapter, or even an eGPU. Typically this would require sacrificing the internal wifi card in favour of USB wifi).

Beware PCIe adapters that take multiple M.2 drives. They seem to fall into three categories:

  1. x4 card with one NVMe slot and one SATA slot (the latter usually a passthrough from a motherboard SATA port - as pictured in another answer)
  2. x4 or x8 card with 2 or 4 NVMe slots, but multiplexing the NVMe traffic through a PCIe switch (reducing your theoretical maximum bandwidth, problematic if you wanted to RAID the cards)
  3. x16 card with 4 true NVMe x4 slots, but relying on PCIe bifurcation support in the chipset and BIOS (usually only available on higher-end boards - although if the chipset supports, it may be possible to patch it into the BIOS).
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The picture shown is adapter card nvme SSD to PCIE x1 and not x4 though. Theoretically that the SSD will function with 1 lane from the x1 slot but nvme SSD need to fully function from an x4 pcie slot.

But I found a much appropriate adapter card not from a x1 pcie slot but from a x4 slot and supports 1 nvme SSD and 1 m.2 data ssd. But my question is, was the x1 converted to x4?or it's just still x1 allowing the ssds to work at x1 lane? enter image description here

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  • I think an x4 card will work with 1 lane too, but it will have reduced bandwith. In the case of pcie 3, you will have around 1GB/s or 8Gbps. Another thing here, that I don't think you can put this into an x1 slot, without cutting the slot or the card. – inf3rno Jan 5 at 8:42
  • Correct you have to cut the slot or the card and it would still only run at 1x speed. This isn't an answer to the question as stated. – Dale Mahalko Feb 17 at 15:43
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A huge THANKYOU to the admin who answered a query that has long been driving me nuts (finding the right search string?) - "can i run a mainstream pcie 3 x4 nvme on a pcie x1 m.2?"

It is a long argument as to why, but a neglected aspect of that debate IMO, is the directness of the pcie cpu/pcie nvme link VS the cpu/sata ssd link, & also the cumbersome legacy of sata's HDD origins.

I, unusually, have some systems w/ 2 spare pcie x1 slots w/ direct links (not chipset lanes). I expect excellent latency from bargain small nvme drives, if not great bandwidth.

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Wow thanks for the response I have also been struggling to find exactly what I need to use my last remaining X1 slot with a M2 nvme(Kingston a2000) on an Asus b460m-a mobo, so I bought a card but stupidly realised when it arrived that it is an x4 not x1. Do I a see if I can buy something online and return original product OR if an adapter available/advisable? I am more than happy to buy from AliExpress by the way....if anyone can help that would be fantastic thank you in advance

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  • If you have a new question, please ask it by clicking the Ask Question button. Include a link to this question if it helps provide context. - From Review – timuzhti Jul 26 at 9:13

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