ART is a replacement for Dalvik, the "runtime" software that has the job of executing Android apps. Dalvik is a virtual machine -- essentially a software version of a computer that lets Android apps run on a variety of hardware -- that's closely related to Oracle's Java technology.
ART is geared to speed things up by reworking a core part of the process. Developers write apps in high-level languages such as Java, and when they build them, the programming tools don't actually create software that runs natively on device hardware. Instead, the tools produce an intermediate version in what's called bytecode. When you run an app, a Dalvik process called just-in-time (JIT) compilation turns that into the native code a device actually executes.
With the ART approach, that software is compiled during installation so it can load faster, according to an Android Police report. That makes Android apps more like native apps, such as those that run on Windows or iOS, but that doesn't require developers to change what they do.
KitKat includes an option to enable ART. But Google's ART introductory page warns that "Dalvik must remain the default runtime or you risk breaking your Android implementations and third-party applications."
ART could arrive in the next version of Android, engineering director Dave Burke told ReadWrite.
"I don't want to make promises but I imagine next release it could be ready. Maybe. We will switch over when it is ready. It is actually quite fast now, and now we are just really optimizing it, and assuming those optimizations go well I assume that we will be ready to switch over at the next opportunity," Burke said. "We could have made tweaks to Dalvik and we decided that actually it was better to start clean. Because Dalvik is pretty old now. It started when Android started and we hadn't worked on it actively."
(Via Android Police)