XPS 8940, M.2 NVMe slots?

My 8940 shipped with a Western Digital NVME PCIe SSD with "B" and "M" keys.

The question is whether "M"-key only, such as Samsung, will fit and work in the motherboard-mounted adapter.

@JNagarya1 Yes, an "M" key SSD will work in the M.2 card slot on the motherboard. The M.2 SSD mounts in what is called the M.2 SSD card slot, not the motherboard-mounted adapter. There are M.2 PCIe adapters that can be installed in the PCIe slots on the motherboard and utilized to mount M.2 SSDs.

@JNagarya1 Samsung Data Migration will not clone if the Samsung SSD is not the target drive. I believe the software checks to see if the target drive is a Samsung drive. 

As far as the documentation is concerned, the XPS 8940 Setup and Specifications has a link to this Dell article.

I'm not looking for an adaptor.

My XPS 8940 came with a Western Digital NVME PCIe card, but it has both "B" and "M" keys, and nothing in the documentation clarifies whether the onboard-slot will take cards with only "M" key.  I replaced it with a 500gb Western Digital -- but would prefer Samsung, as that is the boot drive backup SSD I installed.  Samsung's "Migration" program is the best of the three I've encountered (Samsung, Seagate, and Western Digital); but it won't migrate/clone from between Samsung and Western Digital.

There's already enough confusion over form factors without adding in that lack of information, and thus compounding the confusion.

I do note that another on the site said he added a Samsung 970 to his 8940, so I'm about to order the 970 EVO.

Samsung "Migration" will detect the Western Digital as target drive -- which is 500gb.  But seems only to read the size of a single partition -- 220-ish-gb.

I've cloned Samsung SSD to Samsung SSD, and the software reads the entire target.

@JNagarya1 In the Samsung Data Migration User Manual there is a System Requirements table and the only drives listed as target drives are Samsung drives. I don't think the software will work properly if the target drive is not a Samsung drive. You should try Macrium Reflect Free Edition.

I'll be replacing the Western Digital with a Samsung 970 EVO, so that won't be an issue.

After years of using various major-manufacturer hard drives, I stick with Samsung first, and Seagate second.  The two are about equal, in my estimation.  Western Digital tend to be noisy.

What I still don't get is that the Western Digital is NVME PCIe, but has both "B" and "M" keys.  

I will say that getting the Samsung 970 EVO installed was a weirdly beastly process.  First I tried Macrium, cloning from Western Digital to 860 EVO SSD, then from 860 (OS backup) to 970; it seems that the computer was booting from the 970, but loading from the Samsung 860 EVO SSD. 

Samsung Migration wouldn't work between the 970 and 860, and the 970 wouldn't show in the BIOS. 

Ultimately, I used Mini Tool Partition Wizard, which had the same weird result.

I then took all the drives except the M.2 off line.

I then cloned the Western Digital to a Western Digital laptop hard drive,* through Sabrent USB cable -- which of course took 900 years.  I then cloned from that hard drive to the 970, which of course took 900 years, and it seems to have worked.

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*I replaced the hard drive in my Dell XPS 15 L502X laptop with a 1TB Samsung 860 EVO, and load-time is the difference between second, and 900 years.

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I have yet to put the other drives (OS backup 860 EVO SSD, 2 Seagate 2TB hard drives) back online, so don't know whether that will confuse the system.

Still, I don't get how the Western Digital "M.2" with both "B"" and "M" keys are nonetheless NVME PCIE.

BTW: the Western Digital is "Blue" -- and there are two different ones.  One is fast, one is slower.  The faster is about $5.00 less.  If looking at them, the one to avoid has noting on the cover about speeds; the one to get is the one with "1,700" on the lower left of the cover.  Also, the blue label is to the left; the one to avoid has the blue label to the right.

I learned of those differences from a Corey Holzman video.  In another video he points out the differences between two Western Digital "Black" drives -- one slow, one faster, apparently the same price, and the box covers identical.  The 512GB is slower than the 500GB.

@JNagarya1 Instead of cloning the Western Digital drive with Macrium you should have imaged all the partitions to your hard drive, removed the Western Digital, installed the 970, and then restored the partitions to the 970 by booting from a Rescue Media USB drive you created with Macrium. Cloning should have worked but after cloning and before booting from the 970 you should have disconnected the 860 from the system. If you don't disconnect the 860, to boot from the 970 you should use the F12 Boot Menu to select the 970.

I am why Samsung Migration did not work. Did you boot from the 860 and then try to clone with Samsung Migration to the 970? When did the 970 not show up in the BIOS, after cloning with Samsung Migration?

When the 970 wasn't appearing in the BIOS, I wasn't able to boot from it via F12.

And it didn't work when attempting to clone from the 860 with either Samsung Migration or Macrium.  Cloning with Mini Tool Partition Wizard did "work," sorta, but I don't recall the details.

What did work is essentially as you suggested: I cloned -- with Mini Tool -- to USBed hard drive, then -- with all other drives offline -- from hard drive to 970. 

I've since enabled only the CD/DVD drive; figured I'd wait awhile before enabling the other three drives -- the 860 and two 2TB Seagate hard drives.  It does seem to be working properly.

Another issue is the video card I installed: Asus Geforce 1030: sometimes while watching a video there will be a grey washed-out screen, then it clears itself.  I don't know much about such things, so assume it's frame-rate related.  (It's the DDR5, not the DDR4, which latter has received scathing reviews.)

Too many questions to answer -- yes, booted from 860 to clone to 970.  I ultimately cloned to a Sabrent USB-cabled laptop hard drive, then from that (with all other drives offline) to the 970.  It is now working, and is in the BIOS.