回复：哭问:AS/400应用系统

I knew a little bit. It's used by most chain-stores,or other big retail stores. Kind like an interactive database management system. It's an old OS developed by IBM, but it's still working fine nowadays. Most stores don't like to upgrade it because of the cost of hardware, employee training, etc.

It's not likely to learn it within few days, unless you have a terminal/workstation running that. Go to any bookstore, you will find something to read on AS400.