The soul of the virtual machine

Java's ability to run on many different kinds of computers grew out of software devised decades before - The enduring appeal of Java isn't hard to understand: With Java, you write code once and it can run on almost any modern computer or operating system-PC or Mac, Windows, Linux, OS X, whatever. It works that way because the Java compiler turns the source code into a kind of ersatz machine code that each of these different systems can execute when equipped with the proper run-time software. So different computers running different operating systems can all become, in programmers' parlance, Java virtual machines.