I'm getting around to finally upgrading to 10.8 Mountain Lion from 10.7 Lion and I want to clean install OS X. I have a 27" 2011 iMac with a 1TB HDD that I partitioned into 4 drives and it's been filling up with garbage that I'd like to completely clean up and start with a blank internal drive. I'll probably repartition the drive anyway but I'd like to do all of the Disk Utility tasks while running OS X externally. With that, I know that I need a bootable/recovery drive. So what's the difference between the two? Obviously, I know that I can boot OS X from a bootable drive but what about the recovery drive? After getting this external drive up and running, how will I be able to install OS X onto the internal drive of my iMac from my external drive?