Android


Android is a an operating system used in mobile phone and tablet PCs
it is developed by Google
it is based on Linux kernel , its a free software
android is very user friendly

Versions of android OS :

Alpha                               1.0

Beta                                 1.1 

Cupcake                          1.5

Donut                              1.6

Éclair                               2.0 - 2.1

Froyo                              2.2 - 2.2.3

Gingerbread                 2.3 - 2.3.7

Honeycomb                  3.0 - 3.2.6

Ice cream sandwich    4.0 - 4.0.4

Jelly bean                     4.1 - 4.3.1

Kitkat                             4.4 - 4.4.4

Lollipop                          5.0 - 5.1.1

Marshmallow               6.0 - 6.0.1
Android N  

All most all new model handsets uses android OS





Different mobile phone manufacturing companies have different tools for flashing and software repairing


Android firmwares can be downloaded from http://gsmdownloader.blogspot.in/




Custom firmware installation

procedures:

1. Download custom recovery and custom firmware for the handset
2. Install custom recovery
3. Install custom firmware



1. Download custom recovery and custom firmware for the handset

All android handset have a stock recovery file.
A handset with stock/original recovery is as follows :

stock recovery

What is recovery :
An Android device consists of several pieces of software, which include the
bootloader,
radio,
recovery, and 
system.
The bootloader is the first piece of software that is run when your device turns on — it decides whether to load the recovery, or load Android (“system”) and the radio.
The radio is simply the controller for your antennas, which give you a cellular connection to your carrier’s towers,
The recovery, simply put, is a runtime environment (think “mini operating system”) separate from Android that can perform various system-related tasks. The stock recovery on most Android devices can apply OTA (over-the-air) updates, delete user and cache content (for factory reset purposes), and allow external tools from a microSD card to run functions on the device.
Compared to a full-sized PC, it is most similar to the BIOS in that it is a small piece of software that is independent of the operating system and can control various system settings and functions, but it does not actually perform the same exact tasks. For example, the recovery doesn’t control any I/O functions, which is entirely what the BIOS is about. The recovery also has no power as soon as Android is being loaded.

Custom Recovery Basics

A custom recovery environment will do the same things as the stock Android recovery. However, it will also have additional features. Custom recoveries often have the ability to create and restore device backups. Custom recoveries allow you to install custom ROMs. ClockworkMod even offers a “ROM Manager” app that allows you to access many of these features from a running Android system — this app requires a custom recovery installed to function.

A custom recovery is a third-party recovery environment. Flashing this recovery environment onto your device replaces the default, stock recovery environment with a third-party, customized recovery environment. This is a bit like flashing acustom ROM like CyanogenMod — but, instead of replacing your device’s Android operating system, it replaces the recovery environment.

A custom recovery environment will do the same things as the stock Android recovery. However, it will also have additional features. Custom recoveries often have the ability to create and restore device backups. Custom recoveries allow you to install custom ROMs. ClockworkMod even offers a “ROM Manager” app that allows you to access many of these features from a running Android system — this app requires a custom recovery installed to function.

Popular Custom Recoveries

CWM and TWRP are the two most popular custom recoveries, but other custom recoveries may be available for some devices.

ClockworkMod Recovery (CWM) can create and restore NANDroid backups — backups of an Android device’s entire file system. ClockworkMod offers a ROM manager with a file browser that allows you to easily browse for and install custom ROMs via ClockworkMod Recovery and manage and restore backups. It also has other advanced features that will be useful if you’re installing and dealing with custom ROMs.

CWM recovery

Team Win Recovery Project (TWRP) is a touch-based recovery environment. Unlike other recovery environments — including Android’s default stock recovery, which needs to be controlled with the device’s volume and power buttons — this recovery environment has a touch-based interface you can use by tapping your fingers on on-screen buttons. TWRP even supports themes. Like CWM, TWRP offers ROM installation and backup features the stock recovery environment doesn't.

             TWRP recovery

When and Why to Install a Custom Recovery

These custom recovery environments are most useful when you’re installing custom ROMS on your device, as they provide backup, restore, and ROM-flashing features you’ll need. You’ll need to unlock your device’s bootloader to install a custom recovery on it.

Android does offer a way to create full device backups, although this feature is hidden and requires using an adb command. You don’t need to unlock your bootloader, install a custom ROM, or even root your device to create or restore a full backup.

Install a custom recovery when you’re messing around with custom ROMs, or if you really want powerful backup features. This is often seen as a necessary prerequisite to installing a custom ROM, but it isn’t always required. For example,  installing CyanogenMod with the CyanogenMod installer will also install ClockworkMod Recovery (CWM). Following installation guides for custom ROMs will often involve flashing a custom recovery, although you can flash a custom recovery and continue using the stock Android system if you just want those backup features.

2. Install custom recovery & custom ROM

custom recovery can be installed in the following ways:
     1.without using PC
     2.by using PC

if you are not using a PC , you have to root the device first,
Then download mobileuncle tools & Rom manager
put the downloaded custom recovery in SD card
open mobile uncle or rom manager App
flash the custom recovery using above mobileuncle tool
Then put your custom firmware in the SD card
flash the ROM in zip format with the help of recovery menu (install zip from sdcard)
or flash by using ROM manager


If you are using a PC for installation of a custom recovery file , follow there steps:
1. You dont have to root your handset with the help of a software
2. just flash the custom recovery file into the device by a software (like odin,sp flash tool)
3. Put the downloaded custom ROM in sd card
4. reboot the device to recovery mode(now custom recovery)
5. flash the ROM by the option "install zip from sd card"





Functions of a custom recovery:

• The ability for third-party ROMs to be installed over the stock Android image
• The ability to perform Nandroid backups — these are very good backups that saves literally everything from your personal data to the operating system itself
• The ability to communicate with the Android Debug Bridge, or adb, on a computer for debugging and other developer-type actions, which is otherwise only possible when enablingdeveloper tools within Android
• A more useful and/or visually-pleasing interface for the recovery, which can include touch capabilities or an interface not driven by menu options.