> Critical system processes are process-pairs, where a Primary process does the work, but sends checkpoint messages to a Backup process on another processor. If the Primary process fails, the Backup process transparently takes over and becomes the Primary. Any messages to the process-pair are automatically re-routed.

Right. Process migration was possible, but you're right in that it didn't work like Xen.

> It still runs on (standard?) HPE x86 servers connected to HPE servers running Linux to provide storage/networking/etc.

HP is apparently still selling some HPE gear. But it looks like all that stuff transitions to "mature support" at the end of 2025.[1] "Standard support for Integrity servers will end December 31, 2025. Beyond Standard support, HPE Services may provide HPE Mature Hardware Onsite Support, Service dependent on HW spares availability." The end is near.

[1] https://www.hpe.com/psnow/doc/4aa3-9071enw?jumpid=in_hpesite...