Can't Decide whether I have 2.5" mSATA or M.2 SATA SSD

You can use the model number of the drive to check what type it is.  The model number should be available in Device Manager for the Disk Drives section.

Many of the M.2 PCIe drives are being shipped using the SATA mode.  I was reading an article yesterday which explained the Microsoft native NVMe drivers were so bad it may actually be better to run the drive as SATA.  If my Benchmarking results are even near accurate, I would have to agree.

You might check to see if there are any firmware upgrades for your drive and if any OEM type NVMe drivers are available.  

If you would supply the model number, we could check the drive type.

Open Device Manager and expand the Storage Controllers section.  Does it show a Standard NVMe Controller or SATA controller.

You could also select the drive and then change the view to View by Connection, which will show what controller the drive is on.

Manufacturers determine how M.2 slots are configured.  Dell has it configured to run as SATA or PCIe, at least on some systems.  Your thinking is where mine was two weeks ago.

I am sorry but according to you we can run M.2 PCIe NVMe SSDs using SATA mode. But from what I have found from different sources is that PCIe and SATA SSDs are different and use different controllers and protocols and hence drivers. So, how can we run a PCIe SSD using SATA mode ( I don't even know if we can do that)? Also, I couldn't find any firmware upgrades for my drive and even couldn't find what kind it is using the model number. And even if I suppose that I have a M.2 PCIe NVMe SSD working on SATA mode or even M.2 SATA SSD, will an OEM type NVMe driver be compatible with it?

Also can you explain in what sense were PCIe NVMe SSDs and drivers so bad because from what I know they are clearly superior to SATA SSDs and drivers?

I went to the Device Manger and it says 'Intel Chipset SATA RAID Controller' and 'Microsoft Storage Spaces Controller'. Also, when viewed by Devices by Connection, it says SK Hynix SC300 SATA 256GB under 'Intel Chipset SATA RAID Controller'. And my model number of the SSD is 'FJ6CN61691140CM6G'.

I know that manufacturers configure the motherboard as to which SSD to support - SATA or PCIe. But since I have a 84Whr battery, no place to accommodate 2.5" SATA, only way is to connect the SSD to M.2 socket. So shouldn't the SSD be saying M.2 somewhere or run on a M.2 driver? Also, by my understanding, Dell says in specifications that it only supports PCIe NVMe SSDs or 2.5" SSDs. And, since I ordered it as such from a third party vendor, I feel cheated on getting only M.2 SATA SSD (if it is!) and a SATA RAID Controller.

I can't tie that part number to anything definite.  Since you say it shows as a SC300, it probably is a M.2 SATA drive, but it looks like they do also make a SC300 2.5 " drive.

If you have the battery you ordered and it will not allow a 2.5" drive, they you must have the M.2 SATA.

M.2 is a hardware form factor - Windows knows nothing about it.  M.2 can be PCIe (and within that a drive can be NVMe internally) or it can be SATA -- or the socket can support both (which I believe you'll find your system does - it's keyed for both PCIe AND for SATA).

NVMe is a very new specification - and various drive manufacturers are implementing it in different ways -- meaning that a driver for a Samsung NVMe drive may not (usually will not) work with a Toshiba drive, and vice-versa.

This is particularly true of manufacturers like Samsung which use their own controllers (vs. others like Crucial, etc. that buy controllers from outside comapanies like Marvell, Sandforce, etc.).

From SK-Hynix's website, it appears that ALL the SC300 drives are SATA -- not PCIe/NVMe.  Their designation for the NVMe version is PC300, not SC300.

See above.  M.2 is simply the interface between the SSD and the mainboard - it isn't going to show up anywhere under Windows.

Note that if you change the system from RAID on to AHCI, Windows WILL NOT BOOT without either a complete reload or registry surgery.

If you definitely have the larger battery, you MUST have an M.2 drive - a 2.5" drive won't fit the system.

Thank you Saltgrass and ejn63!! I also think that its M.2 SATA. But its just that it isn't being updated using SK Hynix SC300 M.2 SSD Firmware Update provided by Dell. IF there is no way, I will open the laptop and verify it physically. Then negotiate with the vendor for the price difference between M.2 PCIe NVMe and M.2 SATA.

What happens when you try to apply the update?

A window appears with the list of SK Hynix SSDs I have as shown in the screenshot below

It displays what SSD I have i.e. SK Hynix SC300 SATA SSD 256GB(nothing about M.2) but I can't select it. Also, under the Update column, there is only hyphen(-), not 'Ready' and under Bus column it says 'RAID' rather than 'SATA' as shown in pics of update manual (pic below).

Does it have any effect on not being updated? Also, the updater is SK hynix Firmware Updater 20101P00 for Dell 2.0.4.16. As shown in the screenshot, under FW column it says '20121P00'. So, I also doubt that I have already got a superseded update of the driver. Is this the reason that it is not updating? And, in the update manual, it also says the change that will be made in the update is 'Add device form factor'. So, like I said, if I want to view M.2 in the SSD, I should update. But its not happening.

I'd guess by number you already have newer firmware than what the update provides -- but you will want to call Dell to verify that.

I contacted SK Hynix and they verified it that it is M.2 as per the model number and I have got the latest firmware. That is why it is greyed out. Thankyou for your assistance anyways.