My simplified understanding is that mainframes take vertical OLTP scaling AND system redundancy to the absolute extreme. In any other computer your small numbe

My simplified understanding is that mainframes take vertical OLTP scaling AND system redundancy to the absolute extreme. In any other computer your small number of general purpose CPUs have to handle all the business / application logic plus disk IO, network IO, cryptography, system housekeeping, etc. On a mainframe all those other things are offloaded to specialized coprocessors and the actual business logic gets nearly 100% of the cycles on hundreds of special purpose high frequency water cooled business logic CPUs running at 5+GHz. Also any component can fail and be replaced without downtime or lost transactions. CPUs, RAM chips, entire motherboards, anything at all. You can rebuild it online while your transactions continue. Transactions can be run in duplicate across multiple hardware paths to ensure they are never lost and also verify output correctness. If you set out to build a database server that handles 100 million transactions per hour and never ever goes down, you would end up with a mainframe.