I was deciding to get the base model 21.5" because money is tight for me. I have been hearing the hard drive on the base model is extremely slow, what kind if external hard drive should I buy and what brands should I get? And how does a external hard drive work? I've never had one, I've been seeing SSD externals? How do they work, do I plug it in? Does it automatically sync my stuff from my computer to the external drive? Please help, I want to know what I'm spending my money on. Thank you for your responses!