Honestly mainframes sound like what on-premise aims for. You get uptime and proactive maintenance and stuff just runs. Yet the machine is on your premise and the data belongs to you.
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My wife ran a billing system that was a Motorola based AS/400. It was purchased in 1989/90. An ibm CE would drop by and swap parts every now and again when the computer phoned home.
They retired it in 2013, when a key part for the printer was no longer available.