Android Software Structures

What Is A Bootloader?


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In literal terms, the bootloader is code that is executed before any Operating System starts to run. Bootloaders basically package the instructions to boot operating system kernel and most of them also have their own debugging or modification environment. Think of the bootloader as a security checkpoint for all those partitions. Because if you’re able to swap out what’s on those partitions, you’re able to break things if you don’t know what you’re doing.

As the bootloader kicks off before any piece of software on your device, it makes it extremely processor specific and every motherboard has it’s own bootloader. This is one reason that all Android phones have different custom ROMS developed due to high variance of processing hardware present on the device.

Android Bootloader
Every Android phone has a bootloader that instructs the operating system kernel to boot normally. But you need to understand one thing here that as Android OS is an open source OS and is available on a variety of different hardware, every manufacturer has their own version of bootloader specific for the hardware present in it’s environment. At its most basic level, your Android smartphone is like a hard drive, made of up several partitions. One of those partitions holds the Android system files, another holds all the app data you accumulate (which is how you’re usually able to update without losing all your stuff), and others to do more behind-the scenes stuff.

A lot has been said about bootloaders being “locked” and even the developer-friendly Nexus devices shipped with a locked bootloader (Nexus devices and a couple tablets are easily unlocked with a single command).In fact, a lot bootloaders are locked and encrypted, meaning simple commands like “fastboot oem unlock”, won’t do a thing.

Why are Bootloaders Locked?
A bootloader is usually locked on an Android device because although it’s an open source OS, still the manufacturers want you to stick to their Android OS version specifically designed for the device. In order to apply this concept, manufacturers lock the bootloader. With a locked bootloader on Android devices, it is virtually impossible to flash a Custom ROM and forced attempts void warranty as well as usually end up in bricks. Therefore, the first step is to always unlock the bootloader.

Why keep a bootloader out of reach? One of the biggest reasons is that the carriers and manufacturers don’t want to have to support hacked phones. The other is that a lot of time and money is spent developing these things. HTC Sense ain’t cheap. Neither is TouchWiz. But Samsung and HTC both have managed to find a middle ground with the modding community, and pressure is on other companies to do so as well.
What is a kernel

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A kernel isn't something unique to Android -- iOS and MacOS have one, Windows has one, BlackBerry's QNX has one, in fact all high level operating systems have one. The one we're interested in is Linux, as it's the one Android uses. Let's try to break down what it is and what it does.

Android devices use the Linux kernel, but it's not the exact same kernel other Linux-based operating systems use. There's a lot of Android specific code built in, and Google's Android kernel maintainers have their work cut out for them. OEMs have to contribute as well, because they need to develop hardware drivers for the parts they're using for the kernel version they're using. This is why it takes a while for independent Android developers and hackers to port new versions to older devices and get everything working. Drivers written to work with the Gingerbread kernel on a phone won't necessarily work with the Ice Cream Sandwich kernel. And that's important, because one of the kernel's main functions is to control the hardware. It's a whole lot of source code, with more options while building it than you can imagine, but in the end it's just the intermediary between the hardware and the software.

When software needs the hardware to do anything, it sends a request to the kernel. And when we say anything, we mean anything. From the brightness of the screen, to the volume level, to initiating a call through the radio, even what's drawn on the display is ultimately controlled by the kernel. For example -- when you tap the search button on your phone, you tell the software to open the search application. What happens is that you touched a certain point on the digitizer, which tells the software that you've touched the screen at those coordinates. The software knows that when that particular spot is touched, the search dialog is supposed to open. The kernel is what tells the digitizer to look (or listen, events are "listened" for) for touches, helps figure out where you touched, and tells the system you touched it. In turn, when the system receives a touch event at a specific point from the kernel (through the driver) it knows what to draw on your screen. Both the hardware and the software communicate both ways with the kernel, and that's how your phone knows when to do something. Input from one side is sent as output to the other, whether it's you playing Angry Birds, or connecting to your car's Bluetooth.

It sounds complicated, and it is. But it's also pretty standard computer logic -- there's an action of some sort generated for every event. Without the kernel to accept and send information, developers would have to write code for every single event for every single piece of hardware in your device. With the kernel, all they have to do is communicate with it through the Android system API's, and hardware developers only have to make the device hardware communicate with the kernel. The good thing is that you don't need to know exactly how or why the kernel does what it does, just understanding that it's the go-between from software to hardware gives you a pretty good grasp of what's happening under the glass. Sort of gives a whole new outlook towards those fellows who stay up all night to work on kernels for your phone, doesn't it?
What is CWM


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ClockworkMod, abbreviated as CWM, is a popular custom recovery for Android phones and tablets developed by Koushik Dutta (Koush), a well-known name in the Android dev community. ClockworkMod recovery allows you to perform several advanced recovery, restoration, installation and maintenance operations on your Android device that aren’t possible with the stock recovery, and is one of the most common ways used to gain root access, back up device data, install a custom ROMs, kernels, themes, mods and more. However, for anyone new to Android customization and hacking, some of its options might prove to be a tad confusing. In what follows, we will cover all that this recovery is capable of doing, and how to do it.


About Android Recovery
All Android devices ship with a recovery console that is basically a partition on the device’s internal memory and can be booted into. The stock recovery of almost all Android devices provides a few basic yet handy options that allow you to factory reset your device and also to recover its operating system using an official ROM in zip format, but that’s all you can do with it. That’s where a custom recovery comes handy.

A custom Android recovery basically replaces the stock recovery with one that lets you do all you can do with the stock recovery, plus a plethora of more options to give you a lot more control on your device. With a custom recovery, you can install official and unofficial ROMs as well as other updates including apps, themes, kernels etc. using zip files, wipe not just user data but pretty much every partition on your device, mount the storage card for USB mass storage access without leaving recovery, partition your SD card, wipe Dalvik cache and battery stats, fix permissions, perform, manage and restore backups and so on.


Introduction To ClockworkMod
ClockworkMod recovery is one of the most widely used custom Android recoveries that is available for most mainstream Android devices. It is our custom recovery of choice here at AddictiveTips and almost every custom ROM that we install on our devices is done using this recovery.

ClockworkMod recovery has been developed by Koushik Dutta (also known as Koush) – the same guy who brought us the Android ROM Manager. He can be found at his blog hacking away at Android devices and at Twitter.
What's Firmware


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What the heck is this firmware? Definition of firmware is permanent software programmed into a read-only memory
In Simple words, you can understand it like windows for pc , in case of android we are going to do same thing – installing firmware (Froyo,Gingerbread, ICS, Jelly Bean etc.) on your phone. All phones have their different firmwares and installing tools regard less to the Andriod version (Froyo,Gingerbred). So never think that we can install any firmware on any android phone like we do in PCs.
What is Flashing


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Flashing refers to the overwriting of existing data on ROM modules present in an electronic device with new data. This can be done to upgrade a device or to change the provider of a service associated with the function of the device, such as changing from one mobile phone service provider to another or installing a new operating system.
In simple words flashing is called installing firmware on your phone.
What is Rooting


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When carriers and manufacturers sell you your device, it is almost certain that the device would come with certain software restrictions in place. There are a variety of different reasons why they might do that – some claim that this is done to protect the user, preserve the device’s warranty (this policy will vary from manufacturer to manufacturer), prevent users from getting rid of carrier bloatware apps or simply because the manufacturer would prefer if your device was distinguishable from the competition based purely on its user interface (i.e. Samsung’s TouchWiz, HTC Sense UI, etc).

Whatever their reasoning may be, chances are if you are looking to customize your device on a deeper level, you’d be out of luck and this is where rooting comes into play.

Rooting is essentially a process that allows users of smartphones, tablets or other devices running on Android to gain “superuser” access to the software. This will allow the user to perform administrative tasks such as writing to locations normally restricted by the system which in turn will allow for deeper customization. For iOS users, rooting on Android devices could be thought of as a close equivalent to jailbreaking your device.
What are custom ROM


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A stock ROM is the version of the phone's operating system that comes with your phone when you buy it.

A custom ROM is a fully standalone version of the OS, including the kernel (which makes everything run), apps, services, etc - everything you need to operate the device, except it's customized by someone in some way.
So what does the "customized" part mean? Since Android is open source, developers are free to take stock ROMs, modify them, strip them of garbage, optimize them, add things, and pretty much do whatever their imagination and skills allow.
What is ADB


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According to Google "Android Debug Bridge (adb) is a versatile tool lets you manage the state of an emulator instance or Android-powered device." That certainly sounds like Google, doesn't it? To put it simply, adb is two different applications -- one running on your computer (Windows, Linux or Mac) and one running on your phone. When your phone is connected, and USB debugging is enabled, you can issue commands and communicate with the phone using your computer screen and keyboard.

Your Android phone uses a modified Linux kernel and tools as a base. This means that quite a few Linux commands can be sent via the adb server (the one running on your computer) to the adb client (the one running on your phone) and they will be executed. In our example picture, I've sent the "top" command over the wire to my phone, and my phone sent me back the information and printed it to my terminal.

This can be awfully handy for debugging things that aren't going right, as well sending those weird commands you need when you're hacking away in the middle of the night. Chances are, if you aren't actively debugging something or trying to break hack at your phone, you won't have much use for adb. And that's OK -- there's more than one way to have fun with an Android device.
What's baseband


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Baseband is the Radio or Modem version depending upon the Phone Model, Carrier and Android Software Stack version. The Radio/Modem file is flashed via Recovery tool (other options are ADB/ODIN). The mismatched Radio/Modem and ROM will lead to things not working. You need to find the matching Radio/Modem for the particular ROM you are running.

The radio firmware controls basic low-level functions like network connectivity, Wi-Fi, and GPS. Upgrading Radio firmware will fix connectivity issues, increase range or performance, decrease battery usage, etc. Incorrec tRadio frimeware can disable some functions in your phone such as MMS, 3G Data, VM Notifications, etc. Network operators/carriers select the correct version of the Radio firmware that is suitable for the phone, network and bandwidth.

There is also Modem and Baseband Radio Processor chipsets in Mobile phones. Usually, Google, Phone Manufacturers and carriers develop various types of modem firmware/software that controls the functions of these chipsets.

Firmware is the overall version of the Android system on your phone. Baseband version is the version of the radio embedded in the device. Since Android is based on the Linux operating system, they show you the current version of the Kernel used in the heart of the system. The Build number is just an indicator of which numerical version of the current overall system was built by developers for your device.

You cannot update any of these from the official web site. Updates to the Android system are pushed to the phone over-the-air by the manufacturer or the cell phone carrier. The only other way to update or change an Android phone it to install custom modified ROMs in place of the existing system firmware. That usually requires rooting the phone and a fairly considerable knowledge of how to hack hardware.
source from wikipedia