September 19th, 2010, 12:49 PM
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Join Date: Aug 2010
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FAQ - HBOOT and rooting
Here's some (hopefully useful) information about the bootloader:
It's immediately loaded when the phone is switched on. It's mostly responsible for checking and initialising the hardware and starting the phone's software, for flashing official software releases (RUUs via Fastboot), as well as a few other things. In some ways it's comparable to the BIOS on a PC.
How do I root HBOOT?
You can't, it makes no sense. It's a bootloader, not Android. It's like trying to play a DVD on your kettle.
What does upgrading HBOOT do?
It may add extra hardware support for new phones (e.g. SLCD displays) and may fix a few bugs. HTC doesn't release information about it.
What does downgrading HBOOT do?
The opposite. So, if you flash an SLCD phone with an old version of HBOOT that doesn't have the support, the screen won't work.
But rooting depends on HBOOT version?
Why does upgrading HBOOT remove root?
It doesn't. When you flash an official update your ROM is replaced with an official one, which is why root is lost.
How do I change HBOOT version?
By installing an official RUU/update. There's no other way - the bootloader is protected by the phone's hardware security because a corrupt bootloader means a bricked phone with no way to recover. RUUs contain a version of the bootloader, which is automatically flashed.
Why do I need to downgrade HBOOT to root 0.92?
You don't. You had to downgrade Android because unrevoked3 couldn't root froyo. The new release can, so it works.
Why all the talk about HBOOT then?
Because it is confused with software release, which is the important part. An RUU won't work if the installed software is a higher version (e.g. 1.20.x won't work if you have 1.21.x), and people have mistaken that check for HBOOT version.
What about the xda 0.92 to 0.80 downgrade? It runs on froyo.
It's an engineering/test release from HTC that was leaked. It fakes its software version to 2.09.405.8 so it will run on froyo and downgrade the ROM, so long as you're not on a higher release than that. The process has nothing to do with HBOOT, but it does downgrade the bootloader to 0.80 as a side effect - and results in a dead screen on SLCD phones. It's generally a bad idea to use this hack.
Why would any of this matter?
Because instructions based only on HBOOT version are not reliable. They may not work, or may cause your phone to stop working.
Last edited by teppic74; September 22nd, 2010 at 09:52 AM.