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Comment by classichasclass | Hacker News Reader

This feels like a baby step towards Arm being able to emulate z/Arch workloads, maybe with a bit of secret sauce for certain specific operations, which doesn't seem very much like IBM.

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Not even the weirdest thing IBM did to get compatibility between their mainframes and other CPU architectures. To build the XT/370 and AT/370 expansion cards, they custom-ordered modified 68000s that decoded System/370 instructions instead of the 68k instruction set, with most of the instructions handled by the new microcode and the few stragglers software-emulated:

https://en.wikipedia.org/w/index.php?title=PC-based_IBM_main...

A couple more articles on them.

https://thechipletter.substack.com/p/motorola-intel-ibm-make...

https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro...

I thought about that, too. I think they’re doing this for the same reason IBM has supported Linux LPARs: since a lot of customers who lease System/z currently probably get overprovisioned hardware that they’ll never fully use, why not try a last-ditch attempt to sell the excess capacity as ARM LPARs?

Now you’re thinking like a Big Blue sales rep.

IIRC, they had different licensing prices for cores that would run z/OS workloads and cores that would run Linux on s390x (and other tier for Java, I think). This looks like they’ll have one for Linux on ARM as well.

ARM can emulate z workloads. https://hercules-390.github.io/html/index.html

(or QEMU, for partition level emulation).

Sure. And you can run ARM workloads under QEMU on s390x Linux.

Sure. And you can run ARM workloads in hardware ARM mode.

There's also the poorly advertised IBM-native S390 emulator. I worked on it over a decade ago, you could run S390 on PPC and X86 offically, and ARM and a few others were unofficial.

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