I spent first 15 years of my career at an AS/400 ISV. It is a great system ... for certain things.

I doubt you ordered a "bunch of AS/400's" that is not how it worked and the smallest systems still cost 6 figures. You probably had 1 and you bought a bunch of terminals or something.

The AS/400 has always had to fight for its survival inside IBM because it never drove a lot of the services revenue IBM was trying to grow in the 90's. The AS/400 was famous for being stuck in a closet and running non-stop with maybe a single employee that managed it. It did not sell a lot of IBM consulting and services. IBM mainly sells it via "Business Partners" so there is probably some ISV in the Travel industry that wrote an application that a lot of people used and they are the one selling AS/400's on behalf of IBM to customers that want to use their application.

IBM never made it very easy for developers to learn and support the system on their own. They are too expensive for someone to buy a small one to learn on and the cloud option just did not exist. About all IBM did to help was offer attractive lease options so that companies like mine could afford to have systems to develop our software on.

That said in the early 90's we had to spend over 100K just to buy the tape drives necessary to make "copies" of our software to send to customers. So a customer wants to try our software we have to copy our software on to a tape that probably costs $25+ and then FedEx it to them along with a bunch of heavy 3-ring binders of documentation. It is amazing things ever worked out back then and we survived.

Anyway, I often miss the AS/400. Writing RPG to do transaction processing against DB2/400 always seemed a lot cleaner and more straight forward than SQL and other languages. It also became possible to write real GUI applications though most took the path you described. We rewrote our UI using Eclipse and Java (we were a developer tool). The Java UI talked to the backend API that was still running RPG and ran on the AS/400. I've been gone for 17 years but all that code is still running today.

There are AS/400s that run inventory management type stuff in shops and warehouses that probably haven't been touched in 30-40 years. I'm serious, probably buried under 10 pounds of dust and grease and trash and papers and they just run - they are just sucking down electricity and pumping out data to 5250 terminals over cables.

Granted whatever is running on them could probably run on a Raspberry Pi, but the rewrite would be a 2 million dollar contract by IBM Global Services and the Raspberry Pi would die every 2 years.

I'm curious how much is attributable to the hardware, how much is the software, and how much is simply the fact that no human ever touches it. In a previous life I worked at a CNC machining shop and we had an RS/6000. Everything you say about the AS/400 was also true about the RS/6000. It ran AIX and nobody ever had to think about it because it always worked. But AIX is vastly cheaper than IBM i, and they run on the same hardware now. I think it's worthwhile to examine whether IBM i is actually providing the stability or if it was the hardware + no human touching it the whole time.

Not a scam. I worked on AS/400s for years before I got into more popular operating systems. It's great hardware - very reliable. And although RPG is a pretty weird language, people are very productive on it. You'll still find plenty of largish companies running inventory and other general business software on it to this day.

I have never used or seen an AS/400. I remember that during the late 1980s and early 1990s I worked with some people who used one. After I left that job, I encountered one in a Metro station; she told me that her section had switched to an NT based solution, which was much cheaper but also much more prone to failure. And I did know a guy running an AS/400 perhaps 15 years back. He was very happy with it.