Android 101: What Is A Bootloader?

In this Android 101, we tackle the ‘Bootloader”. 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 Phone Bootloaders ?

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.