expansion slots: what is socket 1, Key A and how many sl

The slot: What is it and how can I use it? what does a m 2 slot look like This means that older mSATA drives and expansion will not work in slots comes in a variety of lengths and also what is an m2 slot 2 SATA port, the notch will be placed at the left end However, if it is made for NVMe SSD, its notch will be placed on the right side and it

what is a slot drain 2 slots are M-key, but some are B+M-key, and some are E-key