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Comment by omnibrain | Hacker News Reader

> the clients inventory system ran on an AS/400 and I knew literally nothing about IBM mainframes

I'm going to be "that guy": The AS/400 (nowadays System i) is not a mainframe but the last standing member of the family of midrange (outside of IBM called minicomputer) systems. (NonStop and OpenVMS - and probably something else I don't know about - are still somewhat around, but nowadays they run on more or less microcomputer systems).

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I'll nitpick your nitpick :)

It's just IBM i now. I believe it was (not including System/38) AS/400-AS/400e->eServer iSeries->eServer i5->System i5->System i->i.

Nonstop has run on X86 systems for about 10 years now, but I don't think they were ever considered 'mid-range'. I think they usually were referred to as mainframes, although the hardware architecture was totally different.

I personally thought the AS/400 was midrange. That's how a co-worker characterized it when he left us to work on OS/400 development (way back in the 1980s).

IBM's own "History of AS/400" web page sort of implies it's midrange:

"For the first time, small businesses, city governments and other medium-size enterprises could set up their own computer networks and connect them to workstations, printers, file servers and even other networks — all running four times faster than what was previously possible."

Maybe System i is more mainframe-y than the original AS/400.

The question got me looking at old AS/400 manuals on bitsavers, and there is some interesting stuff. From the AS/400 handbook:

- Layered machine architecture. This insulates users from hardware characteristics. It enables them to move to new hardware technology at any time, without disrupting their application programs.

- Single-level storage. Main storage and disk storage appear contiguous. An object is saved or restored on the system via a device-independent addressing mechanism

- Operating System, OS/400, is a single entity, fully integrating all the software components (relational database, communications and networking capabilities, etc.)

I agree with you that AS/400/i has always been called mid-range. I was actually referring to NonStop as usually being called "mainframe" not mid-range, or mini-computer, at least the early pre-RISC models. It's another interesting computer architecture.

For more on the AS/400, there's a book by the lead architect of it, Frank Soltis on archive.org that goes into a lot of detail. It is really quite different from anything else.

https://archive.org/details/insideas4000000solt/mode/2up

EDIT: bitsavers has a bunch of Tandem (NonStop) stuff as well.

Ahh.. got it. My old employer also had Tandems in the 1980s, but I didn’t know about the NonStop name.

With 128 bit pointers encoding security and providence information. And a unified memory space, no files, just addresses with RAM as a cache for persistent disks. Might as well be from 2080.

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