So what really are odexed and deodexed ROMs in Android? You may get confused by the terms initially but the difference between the terms is really simple and easy to understand. Once you get what they mean and what role they play in your device, you will know which one suits you better and for what reason. First we need to understand what is .odex file, then we’d be able to understand the difference.

What is .odex file in Android ROM?

ODEx stands for Optimized Dalvik Executable. In any stock Android ROM, you will find some .odex files in addition to .apk files. For example, there will be a Phone.apk as well as Phone.odex for the default phone app. The odex file will contain some parts of the app in compressed form that will be preloaded hence speeding up the boot process. The main purpose of .odex file is to save space and also to speed up the boot process. However, it also makes the process to hack the apk file a bit more complex as the app is divided into to files (.apk and .odex).

Phew! So…

What is Deodex?

It’s the process to take all the packages out from .odex file and reassemble them all together in classes.dex file which is kept inside the APK file.

So, when you go about finding a ROM for your device, you will find plenty of deodexed custom ROMs. Almost all of custom ROMs are pre-deodexed to facilitate theming.

Deodexed vs. Odexed, What’s the Difference, which is Better?

An odexed app boots up faster, a deodexed app is open to customizations. Once you deodex, the app opens up to customizations, you can apply themes. That’s why developers prefer it and most, if not all, of the custom ROMs come pre-deodexed. The advantage of .odex file is the faster load time of the app.