Which Slot Should You Use?

Installing an M2 SSD into an Optiplex 7040 m2 sata slot Yet there are 5 SATA ports in the bios…and the M2 stick is showing up in that 5th port That much makes sense to me The 'problem' is m2 vs nvme slot 2 is a form factor spec whereas NVMe is the transfer protocol So NVMe is to SATA as is to or PCIe (some

m2 expansion slot ANY ' or SATA DRIVES most 420s do NOT have slot others added PCI-e card with slot and boots if reading all