Software Updates in devices

Question

I want to know what is actually happening when we upgrade a device's software. For example we upgrade a device from Android ICS to Jellybean. We do download JellyBean from the server. Then we will install it. My question is: during installation does it replaces the ICS in memory or it resides in separate memory?

I know the Kernel is same for both ICS and JB. Can we downgrade to ICS from JB?

We do have some previous questions on updates, that do answer some parts of your question. For how do updates get to your device, see Who are responsible for pushing out the OTA updates? and How exactly does operating system update work on Android devices?. This question has more info on the actual update process How do I update the OS on my device?. But I don't think we have anything yet on how the actual files are replaced, etc — GAThrawn, May 16 '13 at 14:22
Also related are Why aren't the manufacturers updating the phone to the latest Android version when it's available? and Revert Android Update 4.0 to 3.0/3.2 — GAThrawn, May 16 '13 at 14:26
And as a short answer to your first direct question: an update replaces the previously installed version. So before you ask: a factory-reset only resets the device to factory settings (it deletes all user data and user-installed apps), and does not revert to the Android version originally installed. — Izzy, May 16 '13 at 14:45

score 2 · Answer 1 · answered May 16 '13 at 14:58

The new version replaces the old version, just like upgrading to a new Windows version or a new version of Ubuntu on your PC.

Also, it's not the case that the kernel is the same for ICS and JB. ICS uses a Linux kernel based on the 3.0.1 release, whereas JB's kernel is based on 3.0.31. Android-specific patches to the kernel were also added between the two versions, to support new driver features. But you can downgrade a device to an older version if you have a ROM image to downgrade to, whatever kernel versions they use. The only difference the kernel version makes is that if a device wasn't designed to support a particular kernel version, the manufacturer would have to supply device drivers for the target kernel in order to make a suitable ROM.

Software Updates in devices

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