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Comment by r2sk5t | Hacker News Reader

Thanks for the blog post @picture. I worked on emulating the 360/370 instruction set using both an 8086 processor and a bit slice processor, when I was at Big Blue. The hardware and microcode development was insanely complex. This ended up being a shipped product called the XT and AT/370. https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compati...

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BTW, I still have PTSD from EBCDIC https://en.wikipedia.org/wiki/EBCDIC and big and little Endian https://en.wikipedia.org/wiki/Endianness

Sorry for making it worse, but big/little Endian is nowhere near past us: While most architectures are running little endian now, network byte order (used in IP, UDP, TCP, DNS, etc.) is still big endian. Lots of conversion ensues, so htonl(3) and similar standard library calls are very much alive.

EBCDIC you'll only encounter in the mainframe and midrange world, and it's indeed sobering to realize that its encoding makes perfect sense on punchcards, but none whatsoever on any more modern medium.

ARM, POWER, and several other architectures still exist in big-endian, little-endian, and boot-selectable-endian versions; and some otherwise wonderful ARM chips (looking at you TI Hercules!) are big-endian only.

For any that are selectable, I was careful to say running little endian. :) You are right that big endian still exists, I just wanted to express that a significant part of the world is little endian now.

Agreed. I just wish that the TMS570 family supported little endian. Sigh.

How did IBM convince Motorola to modify the 68000 and Intel to modify the 8087? Did IBMers do this work, or Intel and Motorola?

When I was at IBM, we were making x86-based appliances for business software. I thought it would be cool if they used a mainframe CPU instead of x86 for them. It would have been slower, but possibly more reliable. Definitely it could have had some marketing cachet.. On the other hand, we otherwise did not want to eat our own dog-food.

> How did IBM convince Motorola to modify the 68000 and Intel to modify the 8087? Did IBMers do this work, or Intel and Motorola?

IBM had Nick Treddenick, the lead designer of the 68K do the work. His book "Microprocessor Logic Design" covers the development of the "Micro/370" in great detail, including flow charted microcode that looks remarkably similar to the flowcharts in Ken's article (though apparently Treddenick used flowcharts for the 68K microcode prior to moving to IBM. Regrettably I haven't actually read through my copy yet, so I can't give any further details.

Ken, if you see this I highly recommend tracking down a copy to read, I think it's right up your alley.

Ok, I've ordered a copy. Hopefully it's as good as you say :-)

This is intriguing! What was the market for this machine? The PC and mainframe seem so different in their likely users.

Mainframes are expensive and busy running production workloads. Offloading development and test to franken-PC's running 370 emulation had large cost saving potential. Plus, back in those days the IBM sales organization had a ton of power and could sell anything, the margins were always fantastic, and large numbers of sales reps earned more than the IBM CEO.

Thanks! This makes a lot of sense. I worked for an IBM marketing unit in the 1980s so saw some of this up close!

Why suffer with MS-DOS when you could run VM/370 on your PC?

IBM still sells emulators, now software-based, for companies that do mainframe software development. And they are freakishly expensive.

For the rest of us, there is Hercules!

http://www.hercules-390.org/

True, but there's no legal way to run z/OS on it.

I used to be involved in Mini sales (System 36). Selling DOS based PCs was a doddle compared to these singularly sluggish and ridiculously heavy machines.

I'm not sure VM/370 is less suffering. For example, I run MVS in the typical old 3.8j version (the last public domain one, from I think 1981) as an enthusiast, and it's just amazing how little abstraction there was. MS-DOS practically cuddles you, having an actual file system!

it's just amazing how little abstraction there was

That was deliberate and made a lot of sense. The functionality was split between two programs. The VM/370 part emulates the raw machine. CMS is the "operating system" on top of the VM "hardware".

https://en.wikipedia.org/wiki/Conversational_Monitor_System

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