Recovery Mode

Recovery Mode

In Android devices, Recovery is an Android-based, lightweight runtime environment separate from and parallel to the main Android operating system. Recovery's original purpose was:

§  to apply software updates to the device, e.g. OTA updates, and

§  to erase user data and cache, e.g. for troubleshooting or preparing the device for resale (factory reset) and

§  to run (another) external tool from microSD flash memory

Recovery is stored in a disk partition separate from the main Android partitions (boot/kernel, root/system). It contains its own Linux kernel, separate from the kernel of the main Android system. Because of separate kernel+recovery_apps, the device is able to boot into the recovery mode even main system is broken some way. Until this recovery partition is not broken, the user has nice tool to fix the device. The recovery has nothing to do with the rest of the (Android) system, so is completely independent.

The bootloader determines whether to boot Android or Recovery.

Recovery Mode

Custom recovery apps

The open-source community has extended the original Android Recovery system, to add other features:

§  system backup and restore (NANDroid),

§  the ability to apply Android changes that aren't approved by the manufacturers or carriers,

§  improved user interface, including using the touch screen instead of only the volume and power buttons, and

§  runs adbd, to support ADB connections.

The most popular custom recovery is ClockworkMod Recovery. Others are:

§  4EXT

§  Amon Ra Recovery

§  Team Win Recovery Project (TWRP)

Clock Workmod Recovery

Source : XDA