I wonder if we end up with z series running on arm long term.

The value in z series is in the system design and ecosystem, IBM could engineer an architecture migration to custom CPUs based on ARM cores. They would still be mainframe processors, but likely able to be able to reduce investment in silicon and supporting software.

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themafia 4 hours ago | parent [-]

You can run 1960s System/360 binaries unmodified on modern z/OS. The system also uses a lot of "high level assembler" and "system provided assembly macros" making a complete architecture switch extremely painful and complicated.

They called their new architecture "ESAME" for a while for a pretty obvious reason.

	▲	kjs3 21 minutes ago \| parent [-]
		I don't think that would change if the underlying architecture changes; IBM has been committed to backward compatibility for a long time. Some hypothetical future mainframe class IBM ARM would undoubtedly be able virtualize a 360/370/390 without breaking a sweat. And ARM will undoubtedly enable IBM to add custom emulation hardware to their spin on ARM if they need it.