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Dalvik is an open source, register-based virtual machine (VM) that’s part of the Android OS. The Dalvik VM executes files in the Dalvik Executable (.dex) format and relies on the Linux kernel for additional functionality like threading and low-level memory management.
Dalvik is named after a fishing village in Iceland where ancestors of Dan Bornstein, the person who wrote the VM’s original code, lived. Dalvik is designed for fast execution speeds and operatation in resource-constrained environments like those in mobile devices (with limited memory, CPU and battery power). A Dalvik VM is designed to run multiple instances of itself with each instance hosted on its own separate process and running one application each. When one instance crashes, other concurrently running applications don’t suffer.
Although Android apps are written in Java, they are first compiled into the Dalvik Executable (DEX) format to make them run on the Dalvik VM. DEX files are generally smaller than compressed .JAR (Java Archive) files, making them suitable for mobile devices.
The main difference between Dalvik and a typical Java VM is that the former is register-based while the latter is stack-based. Register-based VMs require fewer instructions than their stack-based counterparts. Although the register-based VMs also require more code, they are generally considered to exhibit faster startups and have better performance than stack-based VMs.
The Dalvik source code license is based on the Apache license. That means, it is free to modify and hence attractive to mobile phone carriers.