I have OS X without any 3rd party app's on another partition on another HDD as a kind of backup in case there's any conflicts or problems with the main everyday OS X I use. I needed to run Software Update on the stripped down OS, so while running on the everyday OS I clicked restart and held down the Option key. This allowed me to select the stripped down OS and boot into that OS. I should have gone into System Preferences, Startup Disk to restart into the stripped down OS, and doing that would have avoided my issue! Anyway . . . so now I am booted into the stripped down OS, I run Software Update and it has to restart to complete the Update, BUT the everyday OS is the one that's still selected as my startup disk in System Pref. Software Update restarts and initially it looks like I am in the stripped down OS version as the dock icon setup looks like it's for the stripped down OS, but as I click around the dock icon setup changes to the one on the everyday OS. I open up the App folder and there are many 3rd party app's in it so obvious I am running using the everyday OS. So when Software Update restarted did it complete the Update on the stripped down OS? I know under System Pref, the everyday OS was selected, but how did the Mac restart me into the everyday OS without asking for my username and password? Finally, do you think I have any problems with what has happened? I now know I should have gone into System Preferences, Startup Disk and selected the stripped down OS to restart into the stripped down OS, and doing that would have avoided this whole problem. Any help will be appreciated! Thanks.