Comment by sillywalk

> Stratus was the hardware fault tolerant company. Tandem, our arch rivals, did software fault tolerance. Our architecture was “pair and spare”.

To expand on this, when Tandem switched MIPS from their proprietary processors, the CPUs were duplicated on a board and compared, and if they disagreed, the logical CPU would halt, similar to Stratus. The software-pair backup processes in a different logical CPU would then take over.