Call Stack, Stack Frames, and Program Counter During the program execution, a machine maintains a pointer to the instruction being executed. It’s called Program Counter (or Instruction Pointer). When you call a method (or send a message if we are speaking of Ruby), the program counter is set to the first instruction on the called function (callee). The program somehow needs to know how to get back to the call site once the “child” method has completed its execution. This information is typica...

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