Google has introduced an experimental new runtime, called ART (Android Runtime) with Android 4.4 KitKat promising faster performance and better battery life than the previous Dalvik runtime. The runtime is the part of the Android operating system which runs apps, so it affects the responsiveness of apps upon launching, running and multitasking.
ART (Android Runtime) currently is an experimental feature and in the early stages of development. If you switch from Dalvik to ART on your device, it may break, force close some applications at the moment; however developers are updating their apps to ?x incompatibilities at impressive speed.
Since ART is an experimental feature, it is disabled by default on Android 4.4 KitKat. You can switch to ART from developer options menu in device’s settings.
To switch, go to “About” and tap the build number repeatedly. It will bring the Development menu. From development menu, select the ART option.