What is a Bootloader ??
In general, bootloader is code that is executed before any Operating System starts running. The bootloader is basically a package of instructions to boot operating system kernel and most of them also have their own debugging or modification environment. The bootloader is executed before any other piece of software (eg applications) run on any device, and therefore each of them has a specific processor and each motherboard has its own bootloader. Every Android phone has a bootloader that instructs the operating system kernel to be able to boot normally. Locked bootloader that can only run (boot) one of the OS that is approved. This means that the boot partition each device has a digital signature that has been approved, or Carrier ID (CID) which ter-code (hard-coded) into the OS that matches the value of that code into it's own bootloader.
Why ?? locked Bootloader
Generally locked bootloader on Android as though Android is an open source OS, but manufacturers still want customers to keep using the version of the Android OS that they have designed specifically for each device (eg SONY designed the Android OS for Xperia). Therefore to apply this concept, manufacturers lock the bootloader her. With a locked bootloader on Android devices, it is virtually impossible to flash Custom ROMs and bootloader unlock process will obviously void the warranty and if we fail to do the bootloader unlocking process will cause the cutting-into bricks Bricks: v -
Is it necessary to Unlock Bootloader ??
The answer is quite simple. If we want to root, then wanted to flash Custom ROM after root, then the stock bootloader on the device we need to open first. Simplenya Unlocking the bootloader allows us to install Custom Firmware, Custom ROMs, Custom Kernel, and Custom Recovery (this usually has paketan of custom kernel) on our Android phones.
WARNING -ALWAYS Do with your own risk-
Unlocking the bootloader of Android devices can cause us to lose the garage -Uh garansi-
This in part can also remove devices (formatting) of internal memory on the device (including applications, contacts, SMS and MMS messages, etc.)
* For 2011-2012 Xperia Bootloader Unlocking devices have no effect on the internal memory
* For Xperia devices released which started from 2013 Unlocking the bootloader will format the internal memory
* For other devices (ex: samsung) I do not know: p
Supplement
In order to install Custom ROMs and Custom Recovery (CWM) in addition to clicking unlcok Bootloader, can still be done with rooting, which is the device we use a software exploit that has been discovered by developers far away there: v and include powerful application called Super User. ..
