A long time ago when I got my first computer, I accidentally opened a 32-bit demo with a nice chiptune inside MS-DOS and it worked. I was surprised by how this happens. I was curious to find out how this works behind the scenes. Back in the time I was a little kid and had no clue about programming. This curiosity leads me to discover amazing things I never imagined.
First, let us have a look at the PE header. It starts with the MS-DOS header and contains a 16-bit MS-DOS executable (stub program).