If you have ever heard "AS/400" and thought "that thing from the 80s", this article is for you. IBM i (the modern name of the AS/400) is still running payroll, banking and logistics in thousands of companies. Sooner or later, a .NET developer is asked to talk to it .

By the end of this article you will know how to:

get a free IBM i account and look around it;

create a data queue (the IBM i message queue) and read it from .NET;

call a COBOL program from C# and get its answer back;

let that COBOL program publish a message that your .NET service consumes;

see the whole thing in a small web page .

Everything below was run for real against a free server. The code is a small open-source library plus a demo web app.

1. The vocabulary in two minutes

IBM i / AS/400 : a server with its own operating system. Same machine family, different names over the years.

Library : roughly a schema or a folder .…