A really good detailed article about JVM internals:
http://www.cubrid.org/blog/dev-platform/understanding-jvm-internals
See also:
http://en.wikipedia.org/wiki/Java_bytecode
http://www.javaworld.com/article/2077233/core-java/bytecode-basics.html
http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html
artima.com: Inside the Java Virtual Machine
http://www.cubrid.org/blog/dev-platform/understanding-jvm-internals
See also:
http://en.wikipedia.org/wiki/Java_bytecode
http://www.javaworld.com/article/2077233/core-java/bytecode-basics.html
http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html
artima.com: Inside the Java Virtual Machine