In previous versions of OS X, before Mountain Lion, one could use the System Preference called Software Update to both update the OS (and Apple's own apps) and also view a list of system updates that have been applied. That all changed in Mountain Lion which uses the Mac App Store (MAS) to apply system updates. This how-to shows you how to see those plus all other app updates once again.
In, for example, OS X 10.7 Lion and previous versions, if you wanted to see the OS and Apple app updates that had been applied, you'd go to System Preferences -> Software Update and select the Installed Updates tab. It looked like this:
Image Credit: Dave Taylor
We all got used to that method; it was second nature. However, apparently Apple felt that having two places to update software, one for Mac App Store apps and one for the system was confusing for new customers. So, starting in OS X 10.8, Mountain Lion, Apple put the system updates in the Mac App Store, at the top. (Apple Menu -> App Store.)
Mac App Store Window
The problem, however, is that there is no convenient place, as before, to show a list of applied updates. The tab in that previous window is gone. Here's how to see that list again.
I. Method #1
1. Under the Apple Menu, select About this Mac.
2. Select More Info.
3. In the next window, select System Report.
4. Scroll to the Software section in the left sidebar. Click the disclosure triangle if necessary to reveal the Software list.
In the sidebar, under Software, select Installations.
5. Select Installations.
Close-up of the Software Installations entry in sidebar
II. Method #2
1. Navigate to your Utilities folder found in the Applications folder.
/Applications -> Utilities Folder -> System Information.app
2. Double-click/launch the app called System Information.app.
3. Continue with step #4 above.
Note that you can can resize the columns for easier reading by clicking and dragging the separator at the top, between columns, as well as sort each column by clicking on the column name. Clicking on the Install Date column is a good idea and will show a time-ordered history of all applied updates.
Close-up of the Update list, sorted by Install Date.
With the introduction of the Mac App Store, those apps that were purchased there as well as 3rd party updates will also appear in this list. One way to isolate Apple's, 3rd Party and MAS updates is to sort by the Source column.