I have a mid 2009 15in MacBook Pro, purchased new, which came with 10.6 Snow Leopard and the install disk. I upgraded to 10.7 Lion when it came out, skipped 10.8 Mountain Lion (didn't feel like spending the $20...lame I know) and upgraded straight to 10.9 Mavericks from 10.7 ('cause free). For posterity's sake going forward, I know I could reinstall 10.6 from the disk if I wanted (for some reason...I don't know, Rosetta support maybe?), but could I then upgrade to 10.7 from the 10.6.8 app store, or will it force me to upgrade to 10.9 since that's the latest version? What about speculation on how things will be going forward? When, say, 10.12 comes out, will I still be allowed to go from 10.6 to 10.7 or 10.9 if I want, instead of only straight to whatever the last supported OS for my MacBook Pro is? Basically, should I be creating backup install disks for each OS version to archive, or will I always be allowed to upgrade/install whatever version I want from the app store?