[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] flexfulton:
Some Information On Bootloaders

It seems there are still a few people ending up here in this thread because they are confused by a failure about bootloaders when they try to flash a ROM. I'd like to just share a little information to help the new guys (and the old guys who may not know) understand bootloaders, why they need to update and the order in which they were released.

A bootloader (NOT TO BE CONFUSED WITH BASEBAND) is a piece of firmware on your device that responds when you press the power button on your phone to turn it on. It tells all of the other chips in your phone to turn on and in what order to do so. Basically it's the brains of the phone to get you from an off state to a fully booted on state.

Back earlier this year, there were major problems with a lot of 3rd party ROMs and random reboots. Phones would just reboot themselves for no real reason. Completely unexpected and no one really knew why. Eventually it was determined that older bootloader versions (based on Ice Cream Sandwich) where the culprit for this faily major bug and that many of the users had unstable bootloaders installed.

To ensure that everyone was on the same level playing field and everyone has a good experience an "assert" was added to the updater script in pretty much every ROM. This is basically a little bit of code that runs before your ROM is flashed to make sure you have a bootloader that is accepted as stable. They will not let you flash a ROM if you have a bootloader that is not on their whitelist. Please note it is also possible to have a bootloader installed the is TOO NEW and hasn't yet been added to the assert. Once a new bootloader comes out it takes a while to get merged in with the ROMs as we are seeing with the new bootloader just recently released.

So with that being said, if you are getting the bootloader assert error, you need to update your bootloader to something newer than what you are currently running. Once a newer acceptable bootloader is flashed on your phone, you will be able to freely flash any 3rd party ROM that you wish.

It's generally not a good idea to ever roll back your bootloader to an older version and in some instances can seriously damage you phone. dstruct2k has been working on some fail safe flashables that will prevent you from doing so which is great. It's still a good idea to know the order in which the bootloaders were released though and as mentioned always flash a newer bootloader, never an older one than what you have installed.

I747 - AT&T

Oldest Release - I747UCLEM

I747UCLG1

I747UCLH1

I747UCLH9

I747UCLI5

I747UCDLK3 - Included in the ROM asserts as known good Bootloader

Newest Release - I747UCDMG2 - Included in the ROM asserts as known good Bootloader

I747M - Telus, Rogers, Bell, Fido, Koodo, Sasktel, MTS, and other M devices.

Oldest Release - I747MVLLE8

I747MLALH1

I747MVLLH1

I747MUMLJ1

I747MUMLK3 - Included in the ROM asserts as known good Bootloader

I747MVLDLK4 - Included in the ROM asserts as known good Bootloader

I747MUMLL1 - Included in the ROM asserts as known good Bootloader

I747MVLDMF1- Included in the ROM asserts as known good Bootloader

Newest Release - I747MVLUEMK5 - Included in SOME asserts. Not all ROMs support flashing when this bootloader is installed. If you want to be safe, flash MF1. That will allow you to flash pretty much any ROM to date. Rolling backwards from this bootloader will result in a brick 100% of the time. Don't try this ever.

I also know there are some leaked AT&T bootloaders but I do not know what they are nor am I listing them here as they aren't official at this time.

I have also seen people asking if restoring nandroids will revert bootloaders on you phone or whether or not you can restore a nandroid from an old ROM once you have updated your bootloader. The answers are that a nandroid will NEVER touch your bootloader so you are free to go back. Furthermore, flashing a ROM will never touch your bootloader. The only time a bootloader will be flashed is if you do it manually with the files found here or if you revert back to stock ROM from Samsung via ODIN or Kies. Be careful with the stock Samsung ROMs flashed via ODIN however because you can brick your device if you try to roll backwards.

I hope this helps you out in understanding why you are here and why you need to update your bootloader if you have been told to do so.

Cheers.

If anyone feels that any of the above information is incorrect, inaccurate or not clear enough, please kindly let me know and I will make the necessary adjustments.