Haswell is the 4th generation of the "i" processors. You can tell by the number. The first digit of the four digit number indicates the generation. 4th Haswell, 5th Broadwell, and 6th Skylake. I hate hardwired RAM. Processors are no longer the limiting factor on computers. It is nice to be able to add some RAM. Storage is probably upgradable on all of them. Some will probably be easier than others and you really have to know what you are doing. I would guess the Airs are practically impossible to upgrade on your own.