Don't forget IBM is still selling (and improving) their POWER family, running AIX (which had the low-end eaten away by Linux) and IBMi (which is the only minicomputer family still standing). IBMi is extremely well defended as it's not even fully documented (unlike mainframes) and, therefore, doesn't even have a way to be emulated outside IBM. And I would not be surprised if that "secret sauce" to be kept in an underground facility under a mountain in the middle of a desert, in a completely offline system behind multiple biometric locks.
ARM survived this long because it had a niche others couldn't break into (and still can't) as the highest performance per watt anywhere.
ARM survived this long because it had a niche others couldn't break into (and still can't) as the highest performance per watt anywhere.