[Verizon HTC One (M9)] santod040:
Rom and Firmware 101

Rom:

Read-Only-Memory/Software/OS and it's version/base is what is shown in Settings > About

A rom flash will not change your firmware and a stand alone firmware flash will not change your software/OS.

A rom is simply the operating system software that you are running.

Just updating a rom, does not mean you have updated your firmware.

They are not one in the same and are not updated the same way in the custom rooting and romming arena.

Firmware:

Lower level read-only partitions "firm"ware, as they stay "firm"ly in place without any ability for the end user modify these parts of their device. Modification of firmware is still however possible, just not under normal s-on usage.

However, with s-off, we can upgrade or downgrade firmware as we please.

Your current firmware version can be found as main version in the output of "fastboot getvar all"

Contains things such as: radio.img, modems, aboot/bootloader, splash screen, touch screen driver, etc,..(is not part of a rom)

OTA:

A file sent from HTC/Your carrier to your device.

It checks the device for any changes at all in the /system.

If any are found, it will fail to apply.

This OTA contains patches for existing files you already have.

If those files are not in place, it cannot properly apply them, so it quits.

OTA will also contain firmware updates.

An official OTA is the only way you will ever get an operating system/OS update and firmware update in one, besides an RUU.

Staying Up To Date:

There are a few ways to stay current/up to date: (from easiest to most painful)

1.) Apply firmware when/if posted as a stand alone zip in fastboot/ruu mode and then flash a stock rooted rom or custom rom of choice.

2.) Run Full unrooted/rooted signed/unsigned RUU's when/if they are posted.

3.) Stay stock and take updates as they come...

Firmware packages:

- Full Stock firmware zips (*not the suggested option)

Stock Boot.img/kernel and stock recovery are included.

Your TWRP is will be overwritten by the stock recovery.

The stock boot.img will overwrite your rooted and or custom one, and you will lose any systemless root you might have in place and will need to reflash SuperSu.
​

- No Boot No Recovery firmware zips (*suggested option)

Stock Boot.img/kernel and stock recovery removed.

This way your TWRP is not overwritten by the stock recovery

The stock boot.img is taken out so that the stock unrooted boot.img does not overwrite your rooted and or custom one, since any rom you flash takes care of this anyhow.

If you do flash a stock boot.img over one that has been modified by SuperSu, you will lose root and will need to reflash SuperSu.
​

-No Boot TWRP firmware zips

Stock Boot.img/kernel and stock recovery removed.

This way your TWRP is not overwritten by the stock recovery

The stock boot.img is taken out so that the stock unrooted boot.img does not overwrite your rooted and or custom one, since any rom you flash takes care of this anyhow.

If you do flash a stock boot.img over one that has been modified by SuperSu, you will lose root and will need to reflash SuperSu.

**Latest TWRP recovery included, so that you can flash it at the same time if you need/want to update it.
​

-No Red Text aboot zips

Removes the red text that appears during the splash screen.

This is not actually part of the splash screen, this is part of the bootloader/aboot/hboot.
​

RUU:

An RUU is going to be a complete OS update.

This does not patch the existing files to make a full rom, like an OTA.

This "IS" the FULL rom and also the complete current firmware up to the date of the RUU base being applied.

A full signed stock RUU will wipe out your current root installation.

You would need to reflash SuperSu or root method of choice after applying an RUU.

It will not however, effect s-off/bootloader status.

_________________

Will add more as I have time.

This is a small start to the extent of the questions you have and how much reading you need to do to understand things better.

I'm sorry that I don't have the time to summarize more at this time.

I have a life, a family and a job and this is something I do for fun.

Let's keep it that way! :)