In Android, recovery is a minimal Linux environment including a kernel and a dedicated ramdisk. When this minimal Linux environment boots up, it runs a binary tool, recovery, to enter the so-called recovery mode. The Linux kernel and ramdisk of recovery mode are usually stored in a dedicated bootable partition. In recovery mode, both the kernel and the root filesystem are in memory so it can manage other partitions without any dependencies.
There are two ways to update devices in the field. The first method is to use fastboot protocol through bootloader. The devices can be reflashed using bootloader. In this case, you can boot your device in fastboot mode and flash your device using the fastboot tool from Android SDK. The second way to flash a device is to use the recovery mode. If you boot the devices into recovery mode, you can flash the device using an image file on the storage or providing...