Horizontal screen orientation is when the monitor is wider than it is tall - probably like your computer monitor is now!  You would use this orientation for games like Bubble Bobble, Street Fighter, Mortal Kombat, etc.Vertical screen orientation is when the monitor is taller than it is wide - a "portrait" setup, like a phone screen.  This would be used for games like PacMan, Donkey Kong, 1942, etc.Be sure your monitor set up will match your game board!Cocktail Vertical Boards  (Can be used in upright cabinets with vertical mounted monitors)Upright Horizontal Screen Boards