Indeed. And IBM do, in fact, still make other OSes, contrary to the subhead of the story: zVM/CMS, zOS (MVS), AIX, and whatever they're calling AS/400 these days.

OS/400 is very interesting OS for those interested in OS architectures.

The complete userspace is bytecode based, regardless of the language.

Applications are compiled on installation phase, or when the generated code is deemed not to be valid any longer.

When there was an architecture change for the PowerPC, many installations only required a regeneration of the installed software.

A concept that Microsoft tried with Longhorn and Windows Phone 7. Or we could even say, the model Android almost has as well.

Native Oberon and Inferno also tried a similar approach, to certain extent.

> When there was an architecture change for the PowerPC, many installations only required a regeneration of the installed software.

Unfortunately it wasn't quite that clean in practice. Regen required TIMI to have access to the compilation templates for each program. These were intermediate compilation stages ( bytecode, I suppose ) that it could then translate to the new machine architecture.

However, these templates were often missing, deleted or out-of-sync. So we did an awful lot of recompiling from source, when we could find it...

Thanks for the input.

I only did a bit of AS/400 administration back in 1994's Summer, just logged into the system and started the backup procedure.

I was actually doing Clipper development and the company where I had a Summer job used AS/400 systems for accounting.

Most of I know about OS/400 bytecode system was found looking for compiler technologies a couple of years later.

The thing I find interesting about OS/400 (or whatever it's name is this month) is the single-level store. When your program needs access to the contents of a file, it's just a memory offset. The OS relies on the swapping mechanism to bring those pages into available memory. Which, when you have flat 64 (one could argue 65) bit addressing … why not?

"Everything's a file!"

"No, everything's memory!"

Wait wait wait...so it effectively memory maps all the things?

Mainframe environments are weird.

And OS/400 files are libraries that you need to open, as another example of strangeness.

Or the OS/360 which uses virtualization for all OSs, like Hyper V does on Windows.

The first OS to boot from the hypervisor has master rights, but all OSs are virtualized.

> Or the OS/360 which uses virtualization for all OSs, like Hyper V does on Windows

No, the hypervisor was called VM. According to WP it most frequently ran CMS guests, which was a light weight single-app OS. But could also run OS/360 guests (which predated VM).

AS/400 isn't mainframe. It's midrange; smaller than a mainframe, and not as flexible.

That is why I always call it by the original name. :)

Yep that is also a nice feature.

Android with ART sounds very much like that. They compile the bytecode to native code at installation or major arch change.

AS/400 is now "IBM i".

Which leads us to the great set of names where we have: IBM i, Apple iOS, Cisco IOS

I am wondering if the tagline got changed--it now says IBM doesn't make consumer, desktop operating systems anymore for a reason.

Originally it stated "IBM don't make operating systems for a reason". It's hard to have full confidence in the rest of the article when that's what it leads with.

Ars Technica isn't exactly big on fact checking. These days most of their short articles are rewritten press releases, and most of their long articles are personal opinion/recollection written as if it was reportage.

While they may got the part about the history of AREXX wrong, most of the article is spot on.

The AREXX error was my mistake. I just read the technology transfer part backwards when I was researching. I've already fixed it in the article and updated it.

The original tagline was "IBM doesn't make operating systems anymore for a reason" which could have been debunked by knowing anything about IBM's product line or about 5 seconds of Googling.

Disclaimer: I'm an Ars subscriber and <3 Ars but when my bullshit detector is already off the charts before the article begins ... it makes me wonder how good the article is.

They probably misread the Wikipedia on OS/2, which says:

> In addition, IBM once made a deal with Commodore to license Amiga technology for OS/2 2.0 and above in exchange for the REXX scripting language.

In other words, IBM licensed REXX to Amiga in return for something else (we don't know what).

But who knows if this is true. Apparently IBM and Commodore already had an IP cross-licensing agreement at the time, and had access to their patents. And AREXX apparently did not contain any IBM code.

    In other words, IBM licensed REXX to Amiga in return for
    something else (we don't know what).

I think it was for technology used in the workplace shell (WPS).