What process takes place when a Mac checks for updates? Does software update only compare available updates with installed updates, or does it do that, then proceed to download the uninstalled ones, and offer them as available updates? The reason I ask is because my late 2010 15" MBP, (2.8GHz i7), has OS X 10.6.6 and all updates prior to 10.6.7 installed. When I check for updates it starts downloading with the update status bar not moving, as though it was downloading something very large, possibly 10.6.7. I have another question. Is the stand alone 2011-001 security update compatible with 10.6.6, or is 10.6.7 required? I tried to install that security update, but get the "This volume doesn't meet the requirements for this update" message. The 2011-001 notes say that it is for 10.6.6.