These Computers contain signal processing to derive the symbology for presentation on a Display whether Head Up, Head Down or Helmet Mounted. In many cases the box will contain some or all of the drivers for the display such as Video or CRT Deflection Amplifiers. Older systems will have a wide range of interfaces both analogue and digital to acquire data from such systems as the Air Data, Radar, Inertial Navigation or Flight Management. Nowadays this same information is generally acquired over a databus such as the Mil-Std-1553.