5 ms·

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 B

by r2sk5t 5y ago

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

klelatti 5y ago
This is intriguing! What was the market for this machine? The PC and mainframe seem so different in their likely users.
- r2sk5t 5y ago
  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.
  - klelatti 5y ago
    Thanks! This makes a lot of sense. I worked for an IBM marketing unit in the 1980s so saw some of this up close!
    - rbanffy 5y ago
      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.
      - Koshkin 5y ago
        For the rest of us, there is Hercules! http://www.hercules-390.org/ http://www.hercules-390.org/
        rbanffy 5y ago
        True, but there's no legal way to run z/OS on it.
      - klelatti 5y ago
        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.
      - anyfoo 5y ago
        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!
        PhantomGremlin 5y ago
        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 https://en.wikipedia.org/wiki/Conversational_Monitor_System
r2sk5t 5y ago
BTW, I still have PTSD from EBCDIC https://en.wikipedia.org/wiki/EBCDIC https://en.wikipedia.org/wiki/EBCDIC and big and little Endian https://en.wikipedia.org/wiki/Endianness https://en.wikipedia.org/wiki/Endianness
- anyfoo 5y ago
  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.
  - addaon 5y ago
    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.
    - anyfoo 5y ago
      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.
      - addaon 5y ago
        Agreed. I just wish that the TMS570 family supported little endian. Sigh.
jhallenworld 5y ago
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.
- ChickeNES 5y ago
  > 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.
  - kens 5y ago
    Ok, I've ordered a copy. Hopefully it's as good as you say :-)

by r2sk5t 5y ago

klelatti 5y ago

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

r2sk5t 5y ago
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.
- klelatti 5y ago
  Thanks! This makes a lot of sense. I worked for an IBM marketing unit in the 1980s so saw some of this up close!
  - rbanffy 5y ago
    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.
    - Koshkin 5y ago
      For the rest of us, there is Hercules! http://www.hercules-390.org/ http://www.hercules-390.org/
      - rbanffy 5y ago
        True, but there's no legal way to run z/OS on it.
    - klelatti 5y ago
      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.
    - anyfoo 5y ago
      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!
      - PhantomGremlin 5y ago
        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 https://en.wikipedia.org/wiki/Conversational_Monitor_System

r2sk5t 5y ago

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

anyfoo 5y ago
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.
- addaon 5y ago
  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.
  - anyfoo 5y ago
    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.
    - addaon 5y ago
      Agreed. I just wish that the TMS570 family supported little endian. Sigh.

jhallenworld 5y ago

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.

ChickeNES 5y ago
> 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.
- kens 5y ago
  Ok, I've ordered a copy. Hopefully it's as good as you say :-)