Android devices in the field can receive and install over-the-air (OTA) updates to the system and application software. This section describes the structure of the update packages and the tools provided to build them. It is intended for developers who want to make the OTA update system work on new Android devices and those who are building update packages for use with released devices. OTA updates are designed to upgrade the underlying operating system and the read-only apps installed on the system partition; these updates do not affect applications installed by the user from Google Play.
Modern A/B devices have two copies of each partition, A and B. Devices apply the update to the currently unused partition while the system is running but idle. A/B devices do not need space to download the update package because they can apply the update as they read it from the network. This is called streaming A/B. A/B updates are also know as seamless updates. For more information about OTA updates for A/B devices, see A/B (Seamless) System Updates .
Older devices have a special recovery partition containing the software needed to unpack a downloaded update package and apply the update to the other partitions. For more information, see Non-A/B System Updates .