Java VM Structure To implement the Java virtual machine correctly, you need only be able to read the class file format and correctly perform the operations specified therein. Implementation details that are not part of the Java virtual machine's specification would unnecessarily constrain the creativity of implementors. For example, the memory layout of run-time data areas, the garbage-collection algorithm used, and any internal optimization of the Java virtual machine instructions (for example, translating them into machine code) are left to the discretion of the implementor Two data types - primitives and references "Stack" programming language with random-access memory