January 12, 2011, 5:40 PM — If you've spent some time browsing the aisles of the new Mac App Store, you've probably come across software marked as "Installed"--despite the fact that you didn't purchase it from the store. It's one of the most confusing aspects of the Mac App Store, and one on which Macworld has fielded a lot of questions already.
But the problem can go beyond simple confusion. Though you might be inclined to think that the store has found all of your existing apps and "grandfathered" them into the store, it doesn't mean that you'll be able to get updates for those applications via the Mac App Store itself. And what about those third-party programs that you have installed that don't show up in the Mac App Store? Do you have to repurchase all of those?
While there's no simple answer to the dilemma, let's take a look at the underlying issue that causes this confusion, and then see what you can do about it.
Bundle, bundle, who's got the bundle?
The culprit here is something called a "bundle ID." This is a unique identifier, created by the software's developer, for each application on your computer; the system uses these IDs for storing settings and other information. They look a bit like a Website address in reverse: iTunes's, for example, is com.apple.iTunes. If you look in the Preferences folder inside your home directory's Library folder, you can see the bundle IDs for most if not all of the programs on your computer.
The problem arises from the fact that when the Mac App Store was announced, Apple didn't tell Mac developers who wanted to put their wares in the store whether they should use the same bundle ID for the Mac App Store version that they use for their existing app or create a separate one--never mind that the two versions of the software may be, for all intents and purposes, identical.
When the Mac App Store launches, it apparently scans your computer for a list of those bundle IDs, which it likely pulls from a centralized OS X system called Launch Services. (You can pull up the list yourself with a little Terminal hokery-pokery--scroll down to the comments for the most recent version of the command).
If the store detects an application installed on your system where both the bundle ID and the app's version match the information associated with the app for sale on the store, that app gets marked as Installed. Those are the apps that where the developer chose to use the same bundle ID for the version in the Mac App Store as the one that it sold elsewhere. (Note that those apps do not show up in the list of Purchases that you can access in the Mac App Store.)