Introduction
For a decade, updating Android meant watching a screen that said “Android is upgrading… Optimizing app 1 of 87” for 10–20 minutes while your phone was completely unusable. If the update failed — corrupted download, power loss, bug — your phone might not boot at all.
Seamless updates changed that. Introduced in Android 7.0 Nougat (2016) and borrowed from Chrome OS, seamless updates use dual system partitions (A/B) to install updates in the background while you use your phone. A reboot swaps partitions in seconds. If the update fails, the phone automatically reverts to the working partition.
It’s the feature that made Android updates fast, safe, and reliable. It also took years for most manufacturers to adopt.
How A/B Partitions Work
A seamless-update device has two copies of every critical partition: system, boot, vendor, product. At any given time, one set is active (the slot you’re running from) and one is idle (the slot you’ll update to).
The update process:
- Download: The OTA package is downloaded in the background.
- Install: The update is installed to the idle slot while you continue using the phone normally.
- Reboot: The phone reboots, swapping active and idle slots. The reboot takes seconds — there’s no “optimizing apps” screen.
- Verify: If the new slot boots successfully, it’s marked as good. If it fails to boot (corrupted update, incompatible change), the system automatically reverts to the previous slot.
The result: updates that take ~10 seconds of downtime instead of 10–20 minutes, with automatic rollback protection.
The Storage Cost
A/B partitioning isn’t free. It requires storing two copies of the system partition, which on modern devices can be 4–8 GB. For a 64 GB phone, that’s 6–12% of total storage. For a 32 GB phone, that’s 12–25% — a significant cost.
This is the main reason manufacturers resisted A/B partitioning, especially for budget devices where every gigabyte of storage matters.
Google’s answer was dynamic partitions (Android 10) — instead of fixed-size partitions, the system uses a logical volume manager that allocates space dynamically. This reduced the storage overhead of dual slots.
Adoption
Adoption was slow:
- 2016: Pixel and Android One devices only
- 2017–2018: OnePlus, Nokia, Motorola adopted
- 2019–2020: Xiaomi, Sony, and others adopted
- 2021–2023: Samsung finally adopted with Galaxy S21+
Samsung’s resistance was the biggest hurdle. As the largest Android manufacturer, Samsung’s refusal to implement A/B partitions meant most Android users never experienced seamless updates. Samsung finally adopted the feature in 2021, and A/B partitioning is now standard on all premium Android devices.
Virtual A/B (Android 11+)
Android 11 introduced Virtual A/B — a hybrid approach that uses the dynamic partition system to minimize storage overhead. Instead of two full system partitions, only one copy of most data is stored, and the update uses snapshot technology to track changes. The storage cost of Virtual A/B is a fraction of traditional A/B.
Virtual A/B is now the standard for new devices and has been retrofitted to many existing A/B devices.
The Legacy
Seamless updates solved a problem that had plagued Android for a decade. No more “optimizing apps” screens. No more 20-minute update windows. No more bricked phones from failed OTAs.
It’s a feature users never see — by design. The best infrastructure is invisible.
References
- A/B System Updates technical documentation (source.android.com)
- Virtual A/B Overview (source.android.com, Android 11)
- Android 7.0 Nougat seamless updates announcement (2016)
- Google Pixel update documentation