What can you tell me about AS/400.
AS/400 is a midrange from IBM. It runs an operating system called OS/400. Code on the system is written in COBOL, RPG and a few other languages. The system is menu driven and has a command line.
Clients usually connect to the AS/400 with a 3270/5250 session. Or GUIs might interface with the AS/400, so the user doesn't ever go into the midrange.
What specifically are you looking for?