This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The way to think of bytecode is that it is the binary code for the Java virtual machine. The Java compiler takes your Java source, and compiles it to byte code.
Now, this Java virtual machine, is merely a virtual machine, so when it is loaded into the JVM, it will be compiled again to the native op codes -- which will be different based on the local processor and OS.