DELL Latitude 5500 2nd storage device

NVMe is M.2, not the mini PCIe that the WWAN slot supports -- they're not physically compatible.

It may or may not be possible to add an SSD, but it'll need to be mini-PCIe, not m.2 -- meaning effectively mSATA.  There are not NVMe drives in non-M.2 format.

Note I said M.2 2242 including a picture which is shorter than 2260 & 2280 are you saying it would have to be 2230 to use in WWAN socket ? 

Does the Dell Latitude 5500 even support a second storage, I currently have NVMe 2280 256GB wanting to install but I want a 500GB extra storage by the WWAN socket 

The issue is not the physical dimensions of the card. NVMe drives use a form factor called M.2 (aka NGFF).  Your WWAN socket is an older half-mini PCIe card.  The two connectors are not compatible either physically or electrically.

There is an older type drive called mSATA that did use the older half mini-PCIe format.  That type of drive would fit the connector.  Whether it will work or not is another matter -- it might, but it's not something supported by the system specifications, and it will mean buying a used drive that's likely going to be appreciably more expensive per gigabyte of storage.  mSATA is pretty much dead as far as anything new is concerned, and you'll find 1T the largest ones made (and not very many over 512G -- most are smaller in capacity).

are you 100% sure my Dell Latitude 5500 can’t use M.2 2242 via WWAN ?

My Laptop is 2019 I’m sure the WWAN socket is not mSATA:

this is a somewhat similar laptop 

https://youtu.be/l92BxOz4WbY

It will work definitely.  Maximum supported nvme is Gen3 x2 with b+m key.  Anything higher than gen3 x2 will not be compatible.

It will not be detected in bios, so it cannot become a boot disk.  It will be detected under Windows and used as regular disk.  The disk MUST be formatted before installing.  putting a non-initialized ssd will not be detected in windows.

The speed is slow, it fluctuate very much from 130MB/s to 600MB/s (most of the time at 130MB/s).  At the end average sequential read will not be more than 280MB/s. Using external USB enclosure with this ssd will perform much better than WWAN slot.

Best Gen3 x2 ssd in the market is SN520, but maximum capacity only 512GB.  Kingspec has up to 1TB but the speed is slower than SN 520.  Since WWAN slot has limited the speed, so it doesn't matter if the ssd is fast.

I know I'm a little late to the party, but I would just like to share my experience doing this "upgrade" after 10 months of successful operation. I haven't read all the posts here, so please excuse me if I'm repeating anything.

I actually followed this guide to begin with, and went out & bought a used 2242 WD SN520 M.2 drive. Booting from a Linux live-USB, I ghosted my existing 2280 512Gb SSD to the SN520.

NB: that original 2280 512Gb was replaced soon after with a Samsung EVO 980 Pro 1Tb.

Anyway, with the SN520 512Gb in the WWAN slot, and the Samsung 1Tb in the main SSD slot, I was booting from the SN520, and using the Samsung for my data files.

You might think that sounds backwards, but this is a development machine with a few quite large projects. It's just as important to read/write my data as fast (if not faster) than starting the OS and its applications =)

So that's it, my 5 cents worth.