What is the Java virtual machine?Simple said a JVM is a software module, for executing Java byte code and the byte code into hardware and operating system special instructions.
By doing so, the JVM allows Java programs can be executed in different environment in the first compilation and does not require changes to the original code.
Java's portability is leading to the key enterprises in the application of language: developers don't need for different platforms to rewrite the application code, because the JVM is responsible for translation and optimization platform.32412
A JVM is basically a virtual execution environment, as a byte code instructions: machine, and for assignment to perform tasks and execute memory operations through interaction with the underlying.
A JVM for the Java application after dynamic resource management operation. This means that it is to grasp the distribution and release memory, keep the model consistent thread on each platform,
An executable architecture for CPU mode in application execution place instructions. The JVMdevelopers from the reference tracking object, and they need to be liberated in the system arein long time.
It is not the same when we manage to release the memory -- a non dynamic languages such as C language as the pain point.
You can put the JVM as a special operating system for Java operation; it is the job of the management environment for the Java application. A JVM is basically a virtual interaction withthe underlying execution environment,
As a bytecode instruction machine, and for the distribution of tasks and execute memory operations.
Why can Java cross platform?
Because after compiled Java program code is not to be a hardware system running code, but a 'intermediate code' - byte code. Then different hardware platforms are installed on different Java virtual machine (JVM),
By the JVM to bytecode and then translated into the corresponding hardware platforms capable of performing code, so for Java programmers, do not need to consider what the hardware platform is, so Java can be cross platform.
C or C++ can not cross platform is compiled code on a specific hardware can be directly executed,
Another platform, the code can not be executed in the, but because can be executed directly, so the efficiency of the implementation of the C or C + + to higher than in Java, so Java can cross platform is realized by the JVM.------Reader’s Digest
 B.原文的翻译
什么是Java虚拟机？
简单的说，一个JVM是一个软件模块，用于执行Java应用字节码并且把字节码转化到硬件，操作系统特殊指令。
通过这样做，JVM允许Java程序在第一次编写后可以在不同的环境中执行，并不需要更改原始的代码。论文网
Java的可移植性是通往企业应用语言的关键：开发者并不需要为不同平台重写应用代码，因为JVM负责翻译和平台优化。
一个JVM基本上是一个虚拟的执行环境，作为一个字节码指令机器，而用于分配执行任务和执行内存操作通过与底层的交互。 Java虚拟机英文文献和中文翻译:http://www.751com.cn/fanyi/lunwen_28976.html