Q. When I get the notice of a software update for iOS, there’s usually a link to read about the security content of the update. But where does Apple officially tell you about all other things that change in these upgrades?

A. You can see a list of the new features, added apps, bug fixes and other tweaks Apple has made to each version of its iOS mobile operating system by visiting the iOS Downloads page in the support area of the company’s site. On the iOS Downloads page, click the link for the version of the system you are using on your iPhone, iPad or iPod Touch to see the scope of the changes (like “new emoji” or “transit directions for Japan”) noted in a series of bullet points.

Each version of the system shown on the iOS Downloads page should also display that same link to the update’s security-related information that you see when you use the Software Update setting on your iOS device. The Apple Security Updates page on the company’s site has those details, along with the documentation for all of Apple’s software products like macOS and its various programs, tools for developers and the operating systems for the Apple Watch and Apple TV.

Google posts information about Android news and updates on the Android section of its company blog and in its monthly Android Security Bulletins. While intended for app creators, the Android Developers site also outlines the new features of each new version of the operating system. As the Android software is widely used by several hardware manufacturers and wireless carriers, those companies may have their own list of updates too.

Microsoft’s site has a general guide to the new features in the latest Windows 10 Mobile operating system, as well as regular blog posts. The mobile-devices support area of the site lists the update history for the various Lumia models that run the Windows software for phones.

While not official sources of documentation, many blogs and online forums dedicated to operating systems also offer in-depth reviews of software updates and often do a thorough job of laying out the good, the bad and the buggy changes. Links to a selection of popular Apple-themed blogs can be found here, but Android blogs and those devoted to Microsoft’s offerings (like MSPoweruser, Windows Central and Thurrott) have sections devoted to Windows mobile matters.