[GUIDE] ROM and Kernel definitions

[Golfdriver97]

ROM? What the?!?! Why do people keep misspelling room? And often they capitalize it?

Kernel? What does popcorn have to do with a smartphone?

These answers and more will be addressed here.

The Android Operating System (OS) is based off of Linux and it's kernel. The Linux kernel operates like Unix.

The short definition of a Kernel would be:
A computer program that takes commands from hardware, converting it into a request for the software, and vice versa. Even though a user uses the Kernel with nearly every action, it is something that can't really be seen.

For more detailed information, you can go here: Android A to Z: What is a kernel? | Android Central

Kernels and ROMs can be flashed to your device. Many ROMs that can be downloaded often have a kernel preloaded. You can, however load a kernel independently. Different kernels can offer better battery life, more speed or even a balance between the two. Ensure the kernel you want to load is compatible with your device and Android version.

[WARN]As with anything else, make a Nandroid of your current setup before flashing any ROMs or kernels. This is your failsafe in the event something goes wrong.[/WARN]

As for a ROM: A ROM is a version of the OS. It is a bulk file that has commands for the system image, apps, and other related files and commands. Ice Cream Sandwich, Jelly Bean, KitKat, all ROMs. When someone who is completely stock gets an update to the OS, they are basically flashing a ROM, it is just that the flashing process is controlled by the carrier/OEM.

To make an analogy, your phone would be like a gaming console and the individual games would be like a ROM. ROMs are also kind of like buildings. You always have to start with a base and build up from there. Starting with 'Vanilla' Android, or what would be seen on a Nexus, OEMs take Vanilla, and add their own panache via features, or icon differences, or both.

[INFO]When flashing ROMs, it is always a good idea to wipe your device. Best practice would be to wipe cache, Dalvik, and factory reset.[/INFO]

[TIP]Even users who are bare bones stock, it is still a good idea to reboot into recovery and wipe the cache, as it may contain files that will drive the OS into errors.[/TIP]

Vanilla Android...
This is bare bones stock. Nothing fancy, completely Spartan. It's minimal layout actually helps to keep the ROM from growing in size. Icons and features are at times minor. But, to offset the difference is with minimal extras, there is less to make things go wrong.

OEM Skins...
This is where a manufacturer, say LG, will take Android, and change the look of it by adding their own icons, possibly even changing the order of things in the settings menu, and can add hooks into the ROM itself. A good example of a hook in the ROM would be the Samsung 'Smart' features. Because say the 'swipe to screen shot' is an action tied to a basic command in the ROM, this is why it can't be removed from the ROM itself.

Custom ROMs...
Custom ROMs can be based off of Vanilla Android, or a skinned version, like Touchwiz. In the case of skinned ROMs they can be debloated, or not. Vanilla type customs can have extra features added, or be fairly close to Vanilla. Any of these differences are how developer sees fit.

Further down, I will break down even further the differences between the ROMs.

 

[Golfdriver97]

Skinned ROMs bring a uniqueness all their own. Mainly for looks, but there are some differences that do set them apart. As stated earlier, Samsung's Touchwiz ROMs have the 'Smart' features added.

I will start by showing what Vanilla looks like. As I said before we need a starting point, and starting with Vanilla is as good as any.

The Nexus 5 Homescreen.


The notification shade and Quick Toggle screens.


And the Settings screen.

Like I said, simplistic. Nothing extraordinary about the icons. A Spartan black and white.

Now, shifting to HTC's Sense skin, we will see some coloring, and modifications to the icons, along with additional icons.
Sense ROM screenshots courtesy of Paul627g.

Notice the fact that the background is white, and almost none of the icons are the same from the Vanilla shots. While there is nothing wrong with a little variety, sometimes this does introduce a complication in helping someone troubleshoot over the forums, as some settings may not be in the same place.


The Settings icons.

Here we have homescreens from Sense. The basic icons at the bottom for the phone, camera, etc., are not the same. However, since Chrome is a third party app, that will look the same across all devices.


Here we have Blinkfeed, with it's own dedicated page on the launcher.


And below we have power and reboot options. Now as this is a Sense based ROM, many of the visuals will look familiar to Stock Sense, but with the additional power and reboot options, this opens up more choices than just shutting down the device.





To clarify: A hot reboot is sort of like a half reboot. Meaning the OS is not getting reloaded, just the apps and the framework. This reboot is typically much faster than a Cold reboot.

 

[Golfdriver97]

Below is a sample of a TouchWiz (TW) stock ROM. This is how almost any Samsung out of the box would look.

Photos courtesy of STARGATE

Below is the lockscreen for TW.


Below is a couple shots of the Home screen. The second shot is after menu is clicked, bringing up some options to add to the home screen, or alter it.


Here is where the skinned version of Android can be seen. Both Settings and Quick Toggles have been altered. In settings, none of the icons are the same as Vanilla, and the Quick Toggles have some of the basic toggles and more, all of which have been altered.


The notification shade in TW: They still have the quick settings above the notifications, and the bar is side scrolling. Also present is the persistent brightness slider.


Below is Moto Blurr. What used to be Motorola's version of Android. Aside form icon changes, not much is different from Vanilla and Blurr.
Screen shots courtesy of B. Diddy

 

[Golfdriver97]

Custom ROMs: Typically custom ROMs follow AOSP. Cyanogen, AOKP, Slim, Paranoid; all are based off of Vanilla. Some follow a signed ROM. MOAR is based off of TW, and while it is a TW ROM, it is debloated and offers more customization.


Following screenshots courtesy of Wizzrah:

Below are the screenshots of the home screen and notification shade.


Search and Weather:


Dialer screen and Music screens:


Settings and other app options:


The above is a perfect example of how a custom ROM can be extremely unique.


Below is another example of a custom AOSP ROM, Anthem.
Screenshots courtesy of VDub2174:

Below is the homescreen:


And the settings screen:


And the device information screen:


Note above how the clock is centered and the battery icon is circular. The ability to change those is a functionality built into the ROM. Many custom ROMs have a feature similar to Xposed Framework to allow these minor changes to your device.

Custom ROMs can be one way to keep up with the most current version of Android, even when the OEM no longer supports it. There are many devices that, thanks to developers like CM, are only a version or two behind. As opposed to still being on Gingerbread.

 

[Golfdriver97]

Just one last shout out to those who contributed to this guide. Thank you very much!