When did slots become commonplace? And NVME slots?

When did slots become commonplace? And NVME slots? slot m 2 nvme 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 slot prices Chapter 5, page 34 indicates that there are two SSD slots The one on the right is for a secondary NVMe SSD

slot prices cards with a B Key interface can only fit into a B Key host slot, and likewise for M Key But cards with a B+M Key design can fit in either

slot combo Locate the PCIe slot This slot is usually easy to find in desktops, but in laptops the location will vary Acer ; Acer Aspire VX 15 , 1x 2280 PCIe NVMe ; Acer ConceptD 5 , 2x 2280 NVMe slot ; Acer ConceptD 7 Pro , 2x