Comment by rbanffy

A 4-rack system is about 1.5 racks of CPUs and 2.5 racks of IO. That's a lot of IO for a single computer, all accessible at bus speeds.

Mere mortals such as me, have to make do with cloud-based clusters where the IO is distributed across multiple machines connected by very fast interconnects, but they don't behave as a single machine, nor have the IO always accessible at local bus speeds.

> Mainframes phone home immediately if they detect problems and an IBM service person will be on site the same day to fix it.

The joke usually went like this: technician shows up to fix the machine, operator says "We didn't call you", to what the technician answers "You didn't. Your computer did"