IBM mainframes and Power servers have “partitions” (LPARs). My understanding of how they work, is they actually are software-based virtualisation, but the hypervisor is in the system firmware, not the OS. And some of the firmware is loaded from disk at boot-up, making it even closer to something like Xen-labelling it as “hardware” not “software” is more about marketing (and which internal teams own it within IBM) than than technical reality. Their mainframe partitioning system, PR/SM, apparently began life as a stripped-down version of VM/CMS, although I’m not sure how close the relationship between PR/SM and z/VM is in current releases.

This sounds like running multiple kernels in a shared security domain, which reduces the performance cost of transitions and sharing, but you lose the reliability and security advantages that a proper VM gives you. It reminds me of coLinux (essentially, a Linux kernel as a Windows NT device driver)

Does anyone have more details on how OpenVMS Galaxy was actually implemented? I believe it was available for both Alpha and Itanium, but not yet x86-64 (and probably never…)

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octotoad 3 days ago | parent [-]

AFAIK, Galaxy was exclusive to Alpha, with no equivalent on Itanium, or any other platform.

	▲	p_l 2 days ago \| parent [-]
		Galaxy depended on carefully coded cooperation between kernels plus firmware support, but otherwise was operating exactly like the proposed Multikernel Architecture. The firmware support was mainly there to provide booting of separate partitions, but otherwise no virtualisation was involved - all resources were exclusively owned.