Java Virtual Machine

Usually, however, people do not have hardware Java processors (although such computers have been built.) They have ordinary PCs and Apples.

Now for the clever part: the Java processor can be implemented as software! It is implemented as a program that reads the bytecodes and performs the operations they specify. (This type of program is called an interpreter.) The Java bytecode interpreter is an executable program that runs on whatever computer system you have. Here is a picture showing this:

The "Java interpreter" in the picture is an executable program that is running on the computer system. Each type of computer system has its own Java interpreter that can run on that system. The "Actual Processor" is the actual, hardware, processor chip of that computer system.

(Another) Important Idea: The Java interpreter running on any computer system "looks like" a hardware Java processor chip. It is a Java Virtual Machine.

Any computer system can execute Java bytecode programs if it has a Java interpreter. The Java interpreter has to be specifically written for the specific processor type of the computer system, but once that is done, the computer system can become a Java virtual machine. That is, it looks like a computer with a hardware Java processor chip and can run Java bytecodes.

When a Java program is translated into bytecodes, the bytecodes are exactly the same no matter what computer system is used. This means the bytecodes on a Sun computer can be sent to an Intel based computer and they will run without a problem.