Page Comparison

Mac OS X Mountain Lion (10.8)

1. Open the console window in the Utilities folder, as outlined above.
2. Navigate to /var/log, then click on install.log
3. Scroll all the way to the top of the list, until you see a series of text that says "Install Mac OS X Mountain Lion"
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4. The date next to the text is the install date.

Mac OS X Yosemite and El Captain (10.10 & 10.11)

1. Open the console window in the Utilities folderthe console window in the Utilities folder, as outlined above.
2. Navigate to /var/log, then click on install.log
3. Scroll all the way to the top of the list, until you see a series of text that says "OSInstaller" 
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4. The date next to the text is the install date.