The document discusses the differences between JDK, JRE, and JVM. It states that JDK includes development tools like compilers and debuggers, while JRE only allows running Java programs and does not include development tools. JVM is contained within both JDK and JRE and is responsible for executing Java programs line by line. The document then discusses the internal working of JVM, stating that it behaves as a runtime engine and calls the main method. When a Java program runs, the class files are loaded by the class loader and the bytecodes are saved in the method area. The JVM then produces class objects and uses the stack and registers to execute instructions.