Tandem computers did not run software in lockstep to achieve fault tolerance. They were shared-nothing parallel clusters before shared-nothing parallel cluster

Tandem computers did not run software in lockstep to achieve fault tolerance. They were shared-nothing parallel clusters before shared-nothing parallel clusters were cool, with message-based communication between processes independent of the node each was running on. This gave near-linear scalability as the number of nodes grew. I worked on parallel sorting and parallel data loading back in the 1980s, scaling up to 256 nodes, and Tandem's NonStop SQL developed and commercialized similar parallel database query evaluation in the late 1980s, ahead of its time.