Android applications are stored using APK (Android Package) files which behave exactly as compressed archives. However, these aren't pre-compiled so developers often make use of additional files in order to speed up the boot process.

Just like APK files, ODEX files are also used to store application data. However, the latter are uncompressed so the Operating System is able to parse information faster. In order to expedite the loading process, ODEX files are used to store critical application data. ODEX files are used in conjunction with APK files for applications and with JAR files for frameworks.

How to open ODEX Files

ODEX files can be created and opened with the Google Android SDK (Software Development Kit) and with the Eclipse IDE (Integrated Development Environment) with the ADT (Android Development Tools) plug-in installed. Both are available for the Windows, Mac OS and Linux platforms.

ODEX files can also be "DEODEXED" which means compressing and transferring all the critical application data stored in an ODEX file back into the APK file. This is necessary before making any modification to the application itself, for example, before changing its image files (.pngs).