Why does M.2 have different lengths?

There are two reasons for the different lengths:

1. Different lengths allow SSDs to have different capacities; the longer the SSD, the more NAND flash memory chips, controllers, and DRAM storage chips can be installed. 2230 and 2242 lengths support 1–3 NAND flash memory chips, while 2280 and 22110 can support up to 8 NAND chips. The largest M.2 form factor can reach up to 2TB SSD capacity.

2. The slot space on the system board limits the size of the M.2: some laptops support M.2 SSDs for caching purposes only, and offer limited space for a 2242 M.2 SSD (the 2230 M.2 SSD is even smaller, but in most cases where a 2242 is supported, the 2230 is not needed).