Google is putting new rules in place for Android 11: it’s going to make support for Android’s “seamless update” feature mandatory for devices launching with the new OS. The news comes to us via an Android source code commit first spotted by XDA Developers, which reads, “Require Virtual A/B on R launches.” In English, this means the seamless update system, which requires two partitions (labeled “A” and “B”), will be required on Android R, aka Android 11.
Android’s seamless update system was introduced in Android 7.0 Nougat (it was actually borrowed from Chrome OS) as a way to reduce the downtime caused by OS updates and to offer a recovery mechanism in case an update applies incorrectly. Applying an update to an operating system usually means taking the OS offline for an extended period of downtime. On Android, before seamless updates, the phone would boot into recovery and could be stuck on the “Installing System Update” screen for as much as 25 minutes. That’s a lot of downtime, and during this time you can’t run any apps, see any text messages, or get any phone calls. The downtime happens because updating the system files requires taking the system partition offline, but the seamless update system fixes this by just having a second copy of the system partition.
As referenced in the commit, the two system partitions are called “A” and “B.” Normally they are exact copies of each other. One of the system partitions is online and being used for the phone operating system, and the other one is offline, just sitting there. When it comes time to apply an update, the update is applied to the offline partition first. So if you’re running on system partition A, then it’s system partition B that gets updated. This happens, well, seamlessly, in the background, and while system partition B is having files updated, you can still do all the normal phone stuff on system partition A. Instead of having to stare at a phone locked to an “Installing System Update” screen for 25 minutes, the phone only has an “installing system update” notification that you can ignore.