[Sony Xperia P, U, Sola, Go] bkpaokfc:
What is what (for newbies) :D

What is flashtool :

Flashtool is a desktop application that you can use to flash Sony software on your unlocked Xperia™ device. This is useful if you’ve for example flashed a custom ROM on your device, and want to go change to a standard Sony software. This flash tool can only be used by Xperia™ devices having an unlocked boot loader.

What is bootloader :

What Is A Bootloader?

In literal terms, bootloader is code that is executed before any Operating System starts to run. The concept of bootloaders is universal to virtually all Operating systems that inculcates operating systems on your PC, laptop, smartphones, and other such devices. Bootloaders basically package the instructions to boot operating system kernel and most of them also have their own debugging or modification environment. 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. The iDevices running iOS somewhat share the same hardware specs and hence you don’t see much variance in their bootloaders.

Android 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. We also saw couple of weeks back that Motorola packaged an “eFuse” command in their Android phones, which could brick (permanently turn off) your device in case you tried to flash a Custom ROM.

Why Is Bootloader 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 To Unlock Bootloader On Android Devices?

The explanation to this question is really simple. If you want root, you’d be wanting to flash Custom ROM post-root, and if you want to install a Custom ROM, you’d need to have your stock bootloader unlocked. In simple terms Unlocking the bootloader allows you to install custom Firmware on your Android phone.

What is fastboot mode and flash mode :

Our Plays have two low-level ways of interacting with our computers. The first one is the Flash mode, which alllows us to install complete firmware packages in FTF packages. FTF stands for "FlashTool File", so we need to use the famous Flashtool with them. The second one is the Fastboot mode, which we can use for some maintenance operations. However, the important functions for us are related with kernels: Fastboot allows us to change the kernels of our devices.