programming-for-dummies

Compiling to a Virtual Machine 93
Compiling to a Virtual Machine
The problem with compilers is that they’re difficult to make for multiple
operating systems and processors. The problem with interpreters is that
they need the source code of a program to run, making interpreters unsuitable
for distributing software. To solve both these problems, computer scientists
created a third alternative — a virtual machine.
To protect the source code of a program, a virtual machine lets you compile
your program into an intermediate file called bytecode or pseudocode (also
known as p-code). To make a program run on multiple operating systems,
you need a virtual machine that runs on each operating system, as shown in
Figure 4-3.
Book I
Chapter 4
Programming Tools
Source code
Compiler
Machine code
A compiler normally converts source code directly into machine
code for a specific type of processor.
Source code
Figure 4-3:
A virtual
machine
acts like a
combination
of an
interpreter
and a
compiler.
Virtual machine
for Windows
Compiler
Bytecode
Virtual machine
for Mac OS X
Virtual machine
for Linux
When compiled to bytecode, a program can run on any operating
system that has the bytecode virtual machine installed.