I think a lot of people might say only IBM sells mainframes - the “z” system. It’s designed to work as a single high-availability machine with a focus on I/O s

I think a lot of people might say only IBM sells mainframes - the “z” system. It’s designed to work as a single high-availability machine with a focus on I/O speeds, rather than a PC cluster that implements high availability at the application level and communicates over IP. You can hot swap faulty components without turning it off. I haven’t ever used one, but I believe you write application code without worrying about such details - the hardware and the libraries you link against will just “make it work”. Perhaps my knowledge is slightly off though.