[Motorola Droid RAZR] mad_fitter:
Looking through the forums on this and other devices with 4.4+ ROMs, the question always comes up, what is ART? Well I happened to run across this explanation. This should clarify it to even the noobist of flashers out there, so I felt it should be shared. Hope this helps everyone understand what it is and why not all apps are compatible just yet. :) (credit to XDA member [MENTION=3789188]bippi79[/MENTION] for the great writeup!)

"A quick little post for something we have been working on lately.

Quite a few of you people would have heard about Android Kitkat and the bag of goodies that it brings along with it. One of those important changes though, is very much under the hood. It is called ART or Android Runtime. So what is it, and why is it important to us?

As described by Google, ART is a new Android runtime being introduced experimentally in the 4.4 release. This is a preview of work in progress in KitKat that can be turned on in Settings > developer options. Before this, all these days, every Android application used to run in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executed files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. Now, with Android 4.4, Google has revealed that the Dalvik replacement, called Android Runtime (ART), should improve the performance of Android apps by a huge margin. The early version of ART in Android 4.4 already has been reported to have sped up apps by around 100%, though it is too early to know the whole truth. It might as well be a placebo till then.

ART straddles an interesting mid-ground between compiled and interpreted code, called ahead-of-time (AOT) compilation. Currently with Android apps, they are interpreted at runtime every time you open them up. This is slow. (iOS apps, by comparison, are compiled in native code, which is much faster.) With ART enabled, each Android app is compiled to native code when you install it. Then, when it’s time to run the app, it performs with all the speed and responsiveness of a native app.

Now, a lot of developers as well as enthusiasts will be really interested in this thing. It allows Android developers to continue writing the exact same code, and having their apps work across a wide range of hardware specs and form factors — but now their apps will now run significantly faster, feel more responsive, and your device’s battery life should improve.

And this is where our new website, www.androidruntime.com comes in. Right now, in these initial stages, people are still confused as to which apps can run in ART and which cannot. Our website solves this tiny issue by letting you search for any app, and see if ART supports it or not. Missing an app but you know the answer to the question? You can even contribute and add to the supported app list. We will do a quick verification and update the search results.

Now the website is still in its infancy, but we are sure that a lot of people might be interested in it. So spread the word and do what you guys really do best.

Oh, and have a great weekend!"