Build number

Build numbers are internal tracking numbers used by developers to track versions of software that are frequently updated, such as operating systems. Usage of build numbers came into use at Apple Computer with the release of Mac OS X.

Finding build numbers in macOS / Mac OS X
From the Apple menu, select About This Mac and a dialog box will display the current running version of macOS. Click on the version number and the build number will be displayed next to it. In early versions of Mac OS X, clicking on it again would display the of the Macintosh.


 * For example: Mac OS X 10.1.5 -> Build 5S60a

Mac OS X 10.0.0 through version 10.0.4, as well as the Mac OS X Public Beta, displayed the build number along with the version number in the About This Mac window.