Inside an IBM/Motorola mainframe controller chip from 1981

I was lucky to get to use an IBM 3090 (close to the peak of the bipolar mainframe) with the Computer Explorers troop that met at New Hampshire Insurance.

We used VM/CMS where VM was a virtual machine monitor and CMS was a single-user OS that felt a lot like CP/M or MS-DOS. (I understand CP/M was inspired by CMS) If you have a lot of developers, they all get their own OS and normally they would store their files on "minidisc" images.

Even though the experience wouldn't seem too foreign to somebody who works on the command line today, the I/O was not character based but instead buffered the way the article describes. Applications were built around a model where you program fields on the terminal which get submitted when somebody hits the send button such as the XEDIT text editor

https://www.ibm.com/docs/en/zvm/7.3?topic=zvm-cms-file-edito...

which was functionally similar to the TECO editor you'd see on DEC minicomputers but quite different in implementation. (e.g. 1970's mainframe apps were similar to 1990's web form applications)

Since we had Digital right across the border in Massachusetts, schools and children's museums in my area where saturated with PDP-8, PDP-11 and VAX machines. The computer club (which met at the physics clasroom) at my high school inherited an old PDP-8 when the school got a VAX, it was an unusual system that they were planning to ship to a newspaper that didn't buy it in the end which had terminals that used an ordinary serial connection but could be programmed to behave like the 3270, we didn't have any software that used that feature until I got out the manuals and wrote a BASIC program that would send the control sequences for that mode.

Y'know, that thing about how IBM terminals are really form display machines instead of character streamers actually put something in context for me. Over a decade ago I interviewed at multiple companies whose business included adapting text-based interfaces for the Web. One was MUMPS[0], the other AS/400[1]. My thought was that they were writing shittons of text parsing code for each screen, but had I been hired and trained for the role I would have learned that HTML forms are poorly reimplemented IBM terminals and time is a flat circle.

[0] "AS/400, but it's a hacked-together line of business program turned hospital OS written when Microsoft Access was still in di-a-pers."

No, I don't know if MUMPS actually presents forms in terminal buffered I/O or not.

[1] "Microsoft Access, but it's an enterprise grade server OS written when Windows NT was still in di-a-pers."

"IBM's vintage mainframes were extremely underpowered compared to modern computers; a System/370 mainframe ran well under 1 million instructions per second, while a modern laptop executes billions of instructions per second. But these mainframes could support rooms full of users, while my 2017 laptop can barely handle one person"

Software has gotten complex, folks were running BBS with multiple users 30+ years ago on 286 computers. First multi user machine I used was 386 BSD supporting 50-100 students at once. 486 machines were supporting thousand of users at once. A cheap under $500 server can probably handle 5k hackernew users at once without missing a beat. Love the article, but don't blame the hardware, hardware has grown, software has just grown faster with so much waste as well.

Author here if anyone has questions...

The partnership between IBM and Motorola is something I find intriguing. And I'm not just talking about PowerPC. In the 80s -- long before Hercules -- IBM developed a "mainframe on a card" solution for use in IBM PCs. For a CPU, they commissioned Motorola to build a special 68000 CPU with different microcode that implemented a large subset of the System/370 instruction set. Any instructions that could not be implemented with this custom-schmustom architecture would trap, and be decoded and emulated by a regular 68000 that ran in tandem with the custom one. The resulting architecture was able to run mainframe operating systems and applications very well, providing mainframe developers a benchside testing solution that allowed them to run software still in development without tying up resources on the actual mainframe (which needed to have as much CPU time as possible committed to production workloads in order to be profitable to run).

Still probably cost an arm and a leg, though. The cards weren't sold on their own, but installed inside a PC under the names Personal Computer XT/370 or AT/370:

https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compati...

I've heard on the grapevine that IBM 3274 uses an IBM proprietary microcontroller architecture known as "universal controller" (UC) – https://bitsavers.org/pdf/ibm/microcontroller/universal_cont... – but not sure how true that actually is. In the absence of written documentation–which probably exists somewhere... but nobody has scanned it and posted it online–this stuff is often just people relying on their decades old memories, and sometimes things get garbled with time. Or some people may even have been confused to begin with.

Slightly off topic and not sure if this is allowed but I've a copy of MVS JCL by Doug Lowe and rather than dump it I'd be more than happy to send it free of charge to anyone in the UK.

It's in excellent condition other than a bit of staining on the outer rear cover

https://www.amazon.co.uk/MVS-JCL-370-XA-JES/dp/0911625852

I worked with them for a year or so at an insurance company and particularly liked some of the feature of the ISPF editor. You could hide rows then perform actions on the remaining columns, quirky but very handy when you needed it!

This is really cool! How do you accomplish your research? I'm assuming IBM has some corporate records, but didn't realize they'd be this complete.

Talking about chips, does anyone know what was the feature size in classical DIP-package chips like 4000, 7400, 74LS, 74HC, 74AC series? I googled around, but for example this Wikipedia article [1] has information only on CPUs, but not on simple logic chips.

[1] https://en.wikipedia.org/wiki/Transistor_count

I'm interested in toying around with IBMs current mainframe offerings and found news articles from 2022 about IBM offering mainframs in the cloud as an experiment. I setup an IBM cloud account and looked around at th offered services, but could not find services related to mainframes. Probably need to be a premium customer.

Uh thats sad. I processed one a similar IBM controller unit when I worked in recycling. I tried for 2 weeks to first figure out what the heck it was, and then secondly find a home for it that wasnt scrap.

Ultimately, it was gutted and converted into a mobile workstation.