[General Questions and Answers] LordManhattan:
Custom ROMs

A stock ROM is the version of the phone's operating system that comes with your phone when you buy it.

A custom ROM is a fully standalone version of the OS, including the kernel (which makes everything run), apps, services, etc - everything you need to operate the device, except it's customized by someone in some way.

So what does the "customized" part mean? Since Android is open source, developers are free to take stock ROMs, modify them, strip them of garbage, optimize them, add things, and pretty much do whatever their imagination and skills allow.

Custom ROMs are oftentimes faster, more efficient, and use less memory because:

- the developer ripped out useless garbage, such as carrier installed apps or

- the developer optimized the kernel. For example, an undervolted kernel can provide a much better battery life than the stock one.

You can upgrade to a version of the OS that has not yet been released for your device, or never will be. This is possible in 2 situations:

- A leaked version of the new ROM showed up online, and the developer got on it like the fat kid chasing an ice cream truck.

- A ROM from another phone was ported by the developer to work on yours. For example, G1 and MyTouch 3G users may never see Android 2.1 officially released on their phones, but Cyanogen, one of the most respected Android developers, was able to create a custom ROM running 2.1 for those devices.

ROOTING:

Getting root or rooting your phone is the process of modifying the operating system that shipped with your device to grant you complete control over it.

This means you can overcome limitations that the carriers and manufacturers put on your phone, extend system functionality, and even upgrade it to a custom flavor of Android.

The name root comes from the Linux operating system world, where the most privileged user on the system (otherwise known as Administrator on Windows) is called root.

You have access to alter any system files, use themes, change boot images, delete annoying stock apps, such as Sprint's NFL Mobile live and Nascar Sprint Cup Mobile, and other various native applications that might drive you crazy (Footprints, Voice Dialer, etc).

On most rooted Android devices, you can back up your entire system to an SD card, much in the same way you can image a hard drive. This is great if you’d like to try a new ROM, as you can back up your phone, wipe it completely, flash the new ROM, and if you don’t like it, just restore from your backup to get your device back to exactly how it was before you wiped it.

The easiest way to do this at the moment is by using ROM Manager.

ROM Manager allows you to easily flash a custom recovery image which is what you will need in order to backup and restore your phone. The recovery image is a special program that can be booted into outside of the phone's main operating system, sort of like an OS recovery console on a PC. By default, the recovery image on most Android phones only gives you a few options, mainly related to wiping the phone. Custom recovery images expand upon these options and usually include scripts that can do things like backup and restore your system, fix file permissions, or allow you to flash custom ROMs that the normal recovery image would otherwise reject.

Normally, flashing a custom recovery image requires some command line work, either on your PC, or on a terminal emulator directly on the phone, but Koush's ROM Manager should automatically flash his custom recovery image (known as ClockworkMod Recovery) for you, provided you're on one of the supported phones and that it is already rooted.

Using ROM Manager is pretty simple. Download and install the application from the market, fire it up, and you’ll be prompted to allow the application superuser permissions - make sure you approve it.

The first thing you’ll need to do is flash the ClockworkMod recovery image that I mentioned earlier, which can be done right in the app (it’s the first option). ROM Manager should automatically find the latest version of the right image for your phone, download, and install it - the whole process is seamless.

After that is done, you can simply use the ‘Manage and Restore Backups’, and ‘Backup current ROM’ options to, well, backup your current ROM or restore from an existing backup.

Rooting Guide for Desire HD

Desire HD ROMs