FastBoot --- What is & What for & How to?

What is Fastboot?

Fastboot is a protocol that can be used to re-flash partitions on your device (update the flash file system in Android devices). It is this small tool that comes with the Android SDK (Software Developer Kit), which is an alternative to the Recovery Mode for doing installations and updates.

Not all phones have a fastboot mode that the user can access. It’s turned on with Nexus devices by default as well as a few other phones and tablets and has been enabled by independent Android developers and enthusiasts on some other phones.

What is Fastboot for?

While in fastboot, you can modify the file system images from a computer over a USB connection. Fastboot mode can start on your device even before Android loads, even under the circumstance when Android isn’t installed at all. And because of that, fastboot mode is useful for quick-updating the firmware, without having to use a recovery mode. In fact, it’s the preferred way to initially install the recovery image. Once you set up, you boot to your phone to fastboot and you can flash image files to the internal memory. Flashing a custom recovery like ClockworkMod is a popular use case. The images you flash don’t need to be signed with a particular key, and thus you should use care when flashing. It can also be used for developer operations. Things like erasing partitions and overriding kernel command line options can be done. And all this features make the tool very useful for developing hardware and software solutions, like unlocking the Bootloader of Google’ Nexus.

How to enter Fastboot?

As said, not all phones have a fastboot mode that the user can access. It’s turned on with Nexus devices by default and has been enabled by independent Android developers on some other devices. So before you proceed, one thing is to make sure your device actually have a fastboot mode.
Entering Fastboot also requires the Android SDK (Software Developer Kit), and different USB drivers for Windows computers.
More information, please go to the section relevant.