I have worked with these extensively - my employer uses one for work, and I have written software both in the greenscreen / ILE languages and in the PASE enviro

I have worked with these extensively - my employer uses one for work, and I have written software both in the greenscreen / ILE languages and in the PASE environment / IFS to accomplish certain tasks (e.g. setting up an intranet site with PHP to present pretty-fied reports of what's in the databases). I think one of my favorite things about it is actually IBM's Data Description Specification (DDS) [0]. You use it for the same reason you'd use a `CREATE TABLE` statement in SQL, but the syntax is much more legible / suited for that purpose, and the file is stored permanently (and used to spool up a "physical file" with the given format, where the data is actually stored). Definitely encourage anyone who is curious about these / esoteric OS's in general to look into them - you can get hands on through IBM's "Cloud for Co-Creation and Enablement" (I believe it's been renamed) or PUB400 [1]. [0]: https://www.ibm.com/docs/en/i/7.3?topic=files-describing-using-data-description-specifications-dds https://www.ibm.com/docs/en/i/7.3?topic=files-describing-usi... [1]: https://www.pub400.com/ https://www.pub400.com/