XPS 15 9570: Replacing NVMe SSD

@KraftD  this question comes up a lot, and I've answered it a few times on this forum, but hopefully I can help clear it up for you.

First, yes your current SSD is using NVMe.  And if you were to replace it with the Samsung SSD, that would also use NVMe even if you didn't change that setting at all.  The only reason you would NEED to change that setting would be if you wanted to use Samsung Magician and/or Samsung's own NVMe driver.

In terms of why people talk about SATA here, it's because the RAID/AHCI BIOS setting area is called "SATA Operation" on many Dell systems, even though that setting also affects NVMe SSDs.  The RAID/AHCI option has been around for a very long time, and it seems that Dell didn't update the name of that option when NVMe SSDs arrived, although some very new Dell systems may have improved this.

The difference between the modes is that AHCI directly exposes the underlying storage interface to the OS, whether it's SATA or NVMe.  As a result, the OS you're using has to have native support for those technologies.  When you enable RAID mode, the Intel Rapid Storage controller is enabled.  At that point, the storage device is still using its native interface (SATA or NVMe) to talk to the Rapid Storage controller, but the OS now only sees the Rapid Storage controller, with the backend storage interface to each device abstracted.  This was convenient in the Windows 7 days because Windows 7 does not natively support NVMe, but if you enable RAID mode (and provide the Intel Rapid Storage driver), then suddenly you can run Windows 7 from an NVMe SSD, because the OS just sees a RAID controller and doesn't know or have to care what the backend storage interface to each device is.

Dell has defaulted to shipping their systems in RAID mode for years now just to standardize factory processes.  The reason is that there are some situations where RAID mode is actually necessary.  One is the Windows 7 scenario I just mentioned.  Another is to set up actual RAID virtual disks on systems where that's possible.  And the third is for scenarios involving Intel Optane storage, or its predecessor Intel Smart Reponse.  Both of those only work when the Rapid Storage controller is active.  Using RAID mode does mean that you may have to provide an Intel Rapid Storage driver to Windows Setup if the version you're installing doesn't have a suitable driver built in, which might be the case with systems that are very new relative to the Windows release you're installing.  That wouldn't be the case with AHCI mode since Windows would have native support for NVMe, but since Dell is already having to deal with injecting drivers into their factory builds, adding one more isn't an issue for them.

The only other downsides to running RAID mode are that you can't run Linux (which doesn't have an Intel Rapid Storage driver) and you can't run certain applications/drivers that require direct access to the storage interface in order to operate, i.e. AHCI mode.  Samsung Magician and Samsung's NVMe driver fall into this category.  But Dell doesn't offer very many systems with Linux pre-installed (though they use AHCI mode on those systems) and they're not using Samsung Magician since Samsung only allows that to be used on their retail drives.  So for their perspective, even in scenarios where RAID isn't strictly necessary, it doesn't introduce a downside, and meanwhile they get to standardize their factory build processes.

But if you want to switch to AHCI following steps you've found in order to use Samsung Magician and/or their NVMe driver rather than Microsoft's NVMe driver or Intel's RST driver, then go right ahead.  If not, then you can leave the system in RAID mode and it will still be running in NVMe mode talking to the RST controller.