Everyone knows that Apple operating systems have version numbers, like iOS 13.5.1 or macOS 10.15.5. But have you noticed that Apple operating systems also have build numbers? For instance, iOS 13.5.1 is build number 17F80. But what does that mean?
To see your macOS version and build numbers on a Mac, choose Apple > About This Mac and click the version number. In iOS or iPadOS, go to Settings > General > About and tap Software Version. For watchOS, in your iPhone’s Watch app, go to General > About and look at the Version line.
Although it’s easy to check the build number of any operating system you’re running, Apple doesn’t publish a canonical list of them anywhere. For that information, head to Wikipedia’s iOS Version History, macOS Version History, watchOS, and tvOS articles or look in the MacTracker app (for the macOS build numbers, you’ll need to click through from the version history article to the expanded article about each release).
Apple makes a new build of each operating system at least every night, so there’s a fresh version ready for the engineers each morning. Most of these builds are never released outside the company, so they don’t get an official version number like 13.5.1. But the engineers still need a way to identify a particular build. That’s what build numbers are for. Once you understand how to decode Apple’s build numbers, you can glean additional information about any given release.
Apple’s two main operating system lines, iOS and macOS, have independent version and build number systems. iOS, iPadOS, watchOS, and tvOS share a common system since they are all derived from the iOS code base. (Only Darwin-derived operating systems—macOS, iOS, iPadOS, watchOS, and tvOS—use build numbers. Classic Mac OS and iPod OS didn’t use the same build number system.)
As you know, every Apple operating system release has an official version number, composed of three parts:
Here’s a simple chart to help clarify the official version numbering scheme.
An Apple build number also has three parts:
Major version: Within Apple, the major version is called the .
build train
Minor version: For iOS and its descendants, the minor version tracks with the minor release; for macOS, it tracks with patch releases.
Daily build version: The daily build indicates how many times Apple has built the source code for the release since the previous public release.
To make this crystal clear, look at iOS 13.5.1, which is build 17F80, and macOS 10.15.5 with its supplemental update, which is build 19F101.
One tangentially related note: For macOS Big Sur, Apple updated the major version number to 11 and reset the minor version number to 0. This move may cause problems for some apps that check feature availability by looking up the operating system version. Since macOS’s major version number remained at 10 for so long, some developers got lazy and checked only the minor version number. Needless to say, such sloppy code could break in Big Sur. Luckily, as Howard Oakley explains, Apple has made some effort to mitigate this problem by having Big Sur return 10.16 rather than 11.0 in some situations. This is why apps should check macOS APIs directly for the existence of a particular feature, rather than assume it exists in a specific operating system version just because Apple first included it in that version or an earlier one.