The Program Counter

Each thread of a running program has its own pc register, or program counter, which is created when the thread is started. The pc register is one word in size, so it can hold both a native pointer and a returnAddress. As a thread executes a Java method, the pc register contains the address of the current instruction being executed by the thread. An "address" can be a native pointer or an offset from the beginning of a method's bytecodes. If a thread is executing a native method, the value of the pc register is undefined.