What is Operating System/400 (OS/400)?
Operating System/400 (OS/400) was the OS developed by IBM for the Application Server/400 (AS/400) using a menu-driven interface tied to the relational DB2/400. The 400 series ran from 1988 to 2013. The OS was renamed eServer iSeries in 2000 as internet access was added to the newer application servers and OS releases.
AS/400 was a midrange system marketed to mid-sized organizations like store chains, which meant a step down from a System/370 mainframe also released in 1988 for large organizations like universities and government agencies. OS/400 — just like MVS — was limited to screens with menus and text boxes to enter data. Programmers had to write code using an extensive selection of languages from RPG (Report Program Generator) and COBOL to SQL and Java. At the same time, these programmers had to make the text-only user interface (UI) for the program look good. Compared to many modern OSs with GUIs with lots of bells and whistles, OS/400 looks boring for many users, but the system was robust and secure.
My experience in AS/400 is limited to working as the operator (full console privileges) for a British company with its North American headquarters in Canada. I had no access to the OS — file system, services, memory management or programming. I was responsible for job and printer queues, opening and closing point of sale (POS) terminals, troubleshooting issues with (dumb) terminals, running reports, purchase requests, inventory correction and data entry including day to day deposits throughout the five (5) years I worked with AS/400. Whenever we needed service, we had to contact IBM.
If you are wondering why I am covering OS/400, it is just nostalgia. I used OS/400 at the turn of the century and I really liked my job although the money was not good.