So, I have a 2010 Macbook (the plain white one) that was running on Snow Leopard OS 10.6.8, it was running pretty slow, so I upgraded to Yosemite OS 10.10 the day it came out (purely by accident). This caused a sort of conniption fit on my computer, sooo I backed it up using time machine with a new 2tb hard drive and took it to an apple store and had them 'downgrade' me to Lion OS 10.7.5. My computer has been running so much smoother! I have been able to simply drag and drop stuff from the external hard drive just fine. Now I am starting med school and decided to get a new macbook that will last a little longer than my ancient one. Is there a way to back up my current Lion os and all its files onto the same external hard drive using time machine (simply because it is so easy) without erasing the other time machine already on there? I am curious because I did not pull all my files off of the first time machine file backed up from the Yosemite os. I was wondering if I need to 1.) go back and put all the files drag and drop style onto the computer from the Yosemite time machine file and then time machine it again (because I will have everything off of there, and therefore will not care if it obliterates the old one), or 2.) if I should just drag and drop all files I have created/added since the downgrade to Lion os instead of using time machine, or finally, 3.) time machine will simply integrate all the new files into the old time machine even though I did not put all the files back on (I've sort of been using it as more of a holding tank until I need those certain files rather than sole a back up....), I don't really care about which os is on the time machine file, but I do not want to loose all my files that are on the old one. I'm not very computer savvy and would so appreciate the advice! Thanks!