M vs : What's the Difference?

When did slots become commonplace? And NVME slots? m 2 nvme slot Nowadays, the acronym NVMe is often thrown around willy-nilly To put it simply, it is a protocol that uses the PCIe interface and is much faster than SATA; it m2 slot screw FRONTECH H110 Chipset Motherboard with 2xDDR4 RAM Slots LGA1151 Supports 678th , 14nm CPUs Processors 2xUSB , 4xUSB 4xSATA Slots

m2 nvme slot My M2_1 slot does not seem to be detecting my NVME SSDs, they work fine in the M2_2 slot Does anyone know why? I want to use both M2