For all intents and purposes, PCIe and NVMe are interchangeable.  The system will have shipped with IRST (RAID) ON, but that still allows for both an NVMe and a SATA SSD operating separately.  The only caveat:  if you install both an NVMe (PCIe) and SATA drives, the NVMe must be the boot drive - meaning you will either need to clone the existing drive to the new one or reinstall Windows.  In either case, remove the SATA drive before starting the install or immediately before booting the cloned drive the first time.  Once complete, you can then reinstall the SATA drive and use it for storage.  
Hello there, Actually I need your help in buying the right and compatible SSD for my Dell laptop (Inspiron 3593) it doesn't have optical drive so I'm purchasing a M.2 SSD so can you please help me with that? Like which one should I buy M.2 NVMe or M.2 PCIe... That's only where I'm confused because it shows PCIe/SATA support in bios and that's why I'm confused because is PCIe support means only PCIe SSD or is it also for NVMe SSD? The point is...I want to know that does my laptop supports M.2 NVMe SSD according to bios also? And I also attached some photographs so that you can see what I mean to ask you. You can see in the Bios photo, it has "AHCI" option and a "Raid on" option...but above that there also an option of M.2 PCIe/SATA ssd option...and all of that makes me more confused that which SSD is compatible for my laptop NVMe or PCIe I would really appreciate your help and will be thankful to you. [IMAGE] [IMAGE]  [IMAGE] 
Dell Inspiron 3593 SSD Upgrade