NOP stands for (and is pronounced) no op, as in no operation. The NOP causes the processor to do absolutely nothing. What's it good for? Filling space. The 8080 can usually execute a bunch of NOP instructions without anything bad happening
Charles PetzoldComputer monitors can operate in many different video modes. In most cases, the decision about how many pixels and colors to display is yours - but not always.
Charles Petzold