@jalefkowit Around time of the failed ports of NSK to Alpha and then to Itanium, the redundancy switched from being hardware lockstep to firmware. (None of the commodity processors support lockstep.)

The NSK product line and most of the HP “server” business (and whatever little was left of DEC) was eventually ceded to HPE.

Here is some info on the post-Tandem-hardware commodity designs, from 2008:

availabilitydigest.com/public_