[Optimus L3, L5, L7 General] -CALIBAN666-:
Maybe some things are a lil bit old but everytime gold,lol.

Work in progress.......

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What is a kernel?

If you spend any time reading Android forums, blogs, how-to posts or online discussion you'll soon hear people talking about the kernel. 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?

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What is a Nandroid backup?

If you've read about hacking or rooting your Android phone (or tablet, or media player) you've seen the word Nandroid used. When tinkering with your device, there's always a very good chance you'll be left with firmware that won't boot, leaving you in a bit of a lurch. A Nandroid backup can mean the all the difference here.

What it is, is a full backup of partitions on your device's NAND flash (NAND stands for NOT AND, a type of electronic logic gate -- it's like the hard drive of your Android device) storage. Think of it as a snapshot of the current running system, and it can be used to restore that that point at any time. Both user data and system files are backed up, and it's a far cry from what we think of when talking about a traditional backup from other software. In fact, it's something that many folks wish was part of the stock Android recovery. Yes, to preform a Nandroid backup you'll need a custom recovery on your device so that the executable files and scripts are there. These have been left out of the stock recovery, likely over issues that would arise if users can backup proprietary files.

Getting the custom recovery on your device is the hardest part, thankfully. Once installed backing up and restoring with Nandroid is simple, involving nothing more than choosing the option and verifying -- no wires needed. Even if you never plan to hack your phone, flashing a custom recovery and running a Nandroid backup is always a good idea. You can find more information about custom recoveries, as well as methods to install and use them, in the device-specific section for your device in the Android Central forums. Give it a look, and decide if it's something you're interested in doing.

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What is an IMEI?

The IMEI (International Mobile Equipment Identity) number is a unique set of 15 digits used on GSM phones to identify them. Because the SIM card is associated with the user and can be swapped from phone to phone, a method is needed to keep track of the hardware itself, and that's why the IMEI was developed. Math nerds will enjoy the way they are calculated -- the first 14 digits are decided by the GSM association, and the final check digit is computed using what's called the Luhn Formula -- crazy base-8 math that mere mortals like most of us don't understand, nor want to understand. You can see the IMEI of your Android phone by looking in settings > About phone if you're curious. (Or on the box if you still have it. Or under the battery or on the phone itself.

What is this number used for? That's the real question, isn't it. Like the MEID number on CDMA phones (think Sprint and Verizon), the IMEI is used for network control. It's not very common, but your mobile operator can block a phone based on it's IMEI in cases where it's been reported stolen or someone didn't pay the bill. Because it's not easy to change the IMEI of your phone (and maybe even illegal -- check your local laws) it's also used to keep track of phones that were involved in criminal activity, and the UK in particular has a handy database of phones used for these purposes. The IMEI number is also used to specify a phone for wiretapping by federal governments worldwide.

On a lighter note, Android apps can also use your IMEI number. The app will declare that it has access to your personal information, and the IMEI can be used to keep track of the device in a remote database. This sounds pretty scary, but it's an easy way (though not necessarily the best way) for app developers to keep a settings database online for your phone, in their app. Let's say you mark a bunch of favorites in a wallpaper app. Those favorites are kept in a small database file online, and when you reconnect to the app it reads your IMEI number to find your preferences. Not an ideal method, but it's easy.

One last thing -- now that we know a little more about IMEI numbers, they will soon be changing to IMEISV numbers. The use-case scenarios are the same, but the data structure and method of calculation is different. An IMEISV gets rid of the check digit (and its complicated Luhn formulated calculation) in favor of two digits used for software version numbering. Like everything else in the mobile space, network identification changes rapidly.

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What is a bootloader?

What is a bootloader? 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.

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. Or, with a little hackery, you're able to run custom ROMs.

There's a lot of squawking about bootloaders being "locked." Actually, most phones shipped with a "locked" bootloader, including the developer-friendly Nexus devices. (Nexus devices and a couple tablets are easily unlocked with a single command.) No, more accurately, most bootloaders are locked and encrypted, meaning the traditional "fastboot oem unlock" command won't do a thing.

And that's a bone of contention for those who love a manufacturer's hardware and want to tinker with their devices. HTC and Samsung and Motorola -- just about everyone, really -- ships devices with locked and/or encrypted bootloaders. Tinkerers (we really don't like calling 'em "hackers") have to find a way around the encryption, usually with some sort of an engineering bootloader that wasn't supposed to be available to the general public. But in recent months, we've seen HTC provide a free tool that will unlock the bootloaders on a number of its devices, and ASUS just got on board, too. Sony Ericsson recently has provided unlocking tools. Motorola's promised to do so as well, but there's been little movement. LG and Samsung ship with unencrypted bootloaders.

Why keep a bootloader out of reach? Probably the biggest reasons are 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.

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What is Dalvik?

What is Dalvik? We hear that word getting thrown around a lot on the Internet when talking about Android and its inner workings. While there's no easy explanation we can give in just a few paragraphs, we can cover the basics and point you in the right direction if you need to feed your nerdly side. In its simplest terms, Dalvik is a virtual machine that runs applications and code written in Java. A standard Java compiler turns source code (written as text files) into Bytecode, then compiled into a .dex file that the Dalvik VM can read and use. In essence, class files are converted into .dex files (much like a jar file if one were using the standard Java VM) and then read and executed by the Dalvik Virtual Machine. Duplicate data used in class files is included only once in the .dex output, which saves space and uses less overhead. The executable files can be modified again when you install an application to make things even more optimized for mobile. Things like byte order swapping and linking data structure and function libraries inline make the files smaller and run better on our devices. The Dalvik VM was written from square one with Android in mind.

Confused yet? Don't feel bad, geeky programming talk usually has that effect. Think of it this way -- when you build a Java application for your computer, a Java Virtual Machine runs the compiled output of the source code. This is why Java runs on just about any operating system. Dalvik is a mobile-optimized version of a Java Virtual Machine, built with code from the Apache Harmony project, which is open-source and runs better than a standard Java VM would on our limited hardware, designed so that you can run more than one instance of the VM at a time -- ie multitasking. Because Dalvik is open-source, it's also been ported to other operating systems, like the one on the BlackBerry PlayBook. It's pretty damn complicated, pretty damn cool, and Oracle (the company that bought Java from Sun) hates it.

Android uses Dalvik because while the license for the standard Java Virtual Machine is GPL2 (free and open-source), when placed in a mobile device and using the Java Micro Edition, it is not. The big dispute between Google and Oracle is all based around Dalvik. Google claims it was written in a "clean-room" environment without using any of Oracle's code, and Oracle disagrees. We claim to have no idea, we're just glad it works as well as it does.

For more on Dalvik, see the Google I/O website.

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